Patent Description:
<CIT> discloses a patient interface assembly which is configured to deliver pressurized gas to the patient's airways. The patient interface assembly includes a patient interface structure that is configured to sealingly engage the patient's face. The patient interface includes a receptacle. The patient interface assembly further includes headgear configured to support the patient interface structure on the patient's head. The headgear includes a clip that is receivable by the receptacle. The receptacle and the clip together form a multiple stage connection arrangement in which each of the multiple stages corresponds to an interlocked position of the clip in the receptacle. Each stage is associated with a corresponding range of headgear tension.

The airways include a series of branching tubes, which become narrower, shorter and more numerous as they penetrate deeper into the lung. The prime function of the lung is gas exchange, allowing oxygen to move from the inhaled air into the venous blood and carbon dioxide to move in the opposite direction. The trachea divides into right and left main bronchi, which further divide eventually into terminal bronchioles. The bronchi make up the conducting airways, and do not take part in gas exchange. Further divisions of the airways lead to the respiratory bronchioles, and eventually to the alveoli. The alveolated region of the lung is where the gas exchange takes place, and is referred to as the respiratory zone. See "<NPL>.

Examples of respiratory disorders include Obstructive Sleep Apnea (OSA), Cheyne-Stokes Respiration (CSR), respiratory insufficiency, Obesity Hyperventilation Syndrome (OHS), Chronic Obstructive Pulmonary Disease (COPD), Neuromuscular Disease (NMD) and Chest wall disorders.

Various respiratory therapies, such as Continuous Positive Airway Pressure (CPAP) therapy, Non-invasive ventilation (NIV), Invasive ventilation (IV), and High Flow Therapy (HFT) have been used to treat one or more of the above respiratory disorders.

Respiratory pressure therapy is the application of a supply of air to an entrance to the airways at a controlled target pressure that is nominally positive with respect to atmosphere throughout the patient's breathing cycle (in contrast to negative pressure therapies such as the tank ventilator or cuirass).

These respiratory therapies may be provided by a respiratory therapy system or device. Such systems and devices may also be used to screen, diagnose, or monitor a condition without treating it.

A respiratory therapy system may comprise a Respiratory Pressure Therapy Device (RPT device), an air circuit, a humidifier, a patient interface, an oxygen source, and data management.

A patient interface may be used to interface respiratory equipment to its wearer, for example by providing a flow of air to an entrance to the airways. The flow of air may be provided via a mask to the nose and/or mouth, a tube to the mouth or a tracheostomy tube to the trachea of a patient. Depending upon the therapy to be applied, the patient interface may form a seal, e.g., with a region of the patient's face, to facilitate the delivery of gas at a pressure at sufficient variance with ambient pressure to effect therapy, e.g., at a positive pressure of about <NUM> cmH<NUM>O relative to ambient pressure. For other forms of therapy, such as the delivery of oxygen, the patient interface may not include a seal sufficient to facilitate delivery to the airways of a supply of gas at a positive pressure of about <NUM> cmH<NUM>O. For flow therapies such as nasal HFT, the patient interface is configured to insufflate the nares but specifically to avoid a complete seal. One example of such a patient interface is a nasal cannula.

Certain other mask systems may be functionally unsuitable for the present field. For example, purely ornamental masks may be unable to maintain a suitable pressure. Mask systems used for underwater swimming or diving may be configured to guard against ingress of water from an external higher pressure, but not to maintain air internally at a higher pressure than ambient.

Certain masks may be clinically unfavourable for the present technology e.g. if they block airflow via the nose and only allow it via the mouth.

Certain masks may be uncomfortable or impractical for the present technology if they require a patient to insert a portion of a mask structure in their mouth to create and maintain a seal via their lips.

Certain masks may be impractical for use while sleeping, e.g. for sleeping while lying on one's side in bed with a head on a pillow.

The design of a patient interface presents a number of challenges. The face has a complex three-dimensional shape. The size and shape of noses and heads varies considerably between individuals. Since the head includes bone, cartilage and soft tissue, different regions of the face respond differently to mechanical forces. The jaw or mandible may move relative to other bones of the skull. The whole head may move during the course of a period of respiratory therapy.

As a consequence of these challenges, some masks suffer from being one or more of obtrusive, aesthetically undesirable, costly, poorly fitting, difficult to use, and uncomfortable especially when worn for long periods of time or when a patient is unfamiliar with a system. Wrongly sized masks can give rise to reduced compliance, reduced comfort and poorer patient outcomes. Masks designed solely for aviators, masks designed as part of personal protection equipment (e.g. filter masks), SCUBA masks, or for the administration of anaesthetics may be tolerable for their original application, but nevertheless such masks may be undesirably uncomfortable to be worn for extended periods of time, e.g., several hours. This discomfort may lead to a reduction in patient compliance with therapy. This is even more so if the mask is to be worn during sleep.

CPAP therapy is highly effective to treat certain respiratory disorders, provided patients comply with therapy. If a mask is uncomfortable, or difficult to use a patient may not comply with therapy. Since it is often recommended that a patient regularly wash their mask, if a mask is difficult to clean (e.g., difficult to assemble or disassemble), patients may not clean their mask and this may impact on patient compliance.

A problem that can arise in relation to respiratory therapy is that there may be a tendency to over-tighten the patient interface to ensure a tight seal between the mask and the patient's face. As the patient interface is worn for long periods, this may result in formation of pressure sores, particularly in older patients who tend to have thinner and dryer skin that is more susceptible to damage. This is estimated to occur in <NUM>%-<NUM>% of patients. The degree of tightening that is needed for a therapeutically effective seal can be subjective, and prone to human error.

While a mask for other applications (e.g. aviators) may not be suitable for use in treating sleep disordered breathing, a mask designed for use in treating sleep disordered breathing may be suitable for other applications.

For these reasons, patient interfaces for delivery of CPAP during sleep form a distinct field.

Patient interfaces may include a seal-forming structure. Since it is in direct contact with the patient's face, the shape and configuration of the seal-forming structure can have a direct impact the effectiveness and comfort of the patient interface.

A patient interface may be partly characterised according to the design intent of where the seal-forming structure is to engage with the face in use. In one form of patient interface, a seal-forming structure may comprise a first sub-portion to form a seal around the left naris and a second sub-portion to form a seal around the right naris. In one form of patient interface, a seal-forming structure may comprise a single element that surrounds both nares in use. Such single element may be designed to for example overlay an upper lip region and a nasal bridge region of a face. In one form of patient interface a seal-forming structure may comprise an element that surrounds a mouth region in use, e.g. by forming a seal on a lower lip region of a face. In one form of patient interface, a seal-forming structure may comprise a single element that surrounds both nares and a mouth region in use. These different types of patient interfaces may be known by a variety of names by their manufacturer including nasal masks, full-face masks, nasal pillows, nasal puffs and oro-nasal masks.

A seal-forming structure that may be effective in one region of a patient's face may be inappropriate in another region, e.g. because of the different shape, structure, variability and sensitivity regions of the patient's face. For example, a seal on swimming goggles that overlays a patient's forehead may not be appropriate to use on a patient's nose.

Certain seal-forming structures may be designed for mass manufacture such that one design fit and be comfortable and effective for a wide range of different face shapes and sizes. To the extent to which there is a mismatch between the shape of the patient's face, and the seal-forming structure of the mass-manufactured patient interface, one or both must adapt in order for a seal to form.

One type of seal-forming structure extends around the periphery of the patient interface, and is intended to seal against the patient's face when force is applied to the patient interface with the seal-forming structure in confronting engagement with the patient's face. The seal-forming structure may include an air or fluid filled cushion, or a moulded or formed surface of a resilient seal element made of an elastomer such as a rubber. With this type of seal-forming structure, if the fit is not adequate, there will be gaps between the seal-forming structure and the face, and additional force will be required to force the patient interface against the face in order to achieve a seal.

Another type of seal-forming structure incorporates a flap seal of thin material positioned about the periphery of the mask so as to provide a self-sealing action against the face of the patient when positive pressure is applied within the mask. Like the previous style of seal forming portion, if the match between the face and the mask is not good, additional force may be required to achieve a seal, or the mask may leak. Furthermore, if the shape of the seal-forming structure does not match that of the patient, it may crease or buckle in use, giving rise to leaks.

Another type of seal-forming structure may comprise a friction-fit element, e.g. for insertion into a naris, however some patients find these uncomfortable.

Another form of seal-forming structure may use adhesive to achieve a seal. Some patients may find it inconvenient to constantly apply and remove an adhesive to their face.

A range of patient interface seal-forming structure technologies are disclosed in the following patent applications, assigned to ResMed Limited: <CIT>; <CIT>; <CIT>.

One form of nasal pillow is found in the Adam Circuit manufactured by Puritan Bennett. Another nasal pillow, or nasal puff is the subject of <CIT>), assigned to Puritan-Bennett Corporation.

ResMed Limited has manufactured the following products that incorporate nasal pillows: SWIFT™ nasal pillows mask, SWIFT™ II nasal pillows mask, SWIFT™ LT nasal pillows mask, SWIFT™ FX nasal pillows mask and MIRAGE LIBERTY™ full-face mask. The following patent applications, assigned to ResMed Limited, describe examples of nasal pillows masks: International Patent Application <CIT> (describing amongst other things aspects of the ResMed Limited SWIFT™ nasal pillows), <CIT> (describing amongst other things aspects of the ResMed Limited SWIFT™ LT nasal pillows); International Patent Applications <CIT> and <CIT> (describing amongst other things aspects of the ResMed Limited MIRAGE LIBERTY™ full-face mask); International Patent Application <CIT> (describing amongst other things aspects of the ResMed Limited SWIFT™ FX nasal pillows).

A seal-forming structure of a patient interface used for positive air pressure therapy is subject to the corresponding force of the air pressure to disrupt a seal. Thus a variety of techniques have been used to position the seal-forming structure, and to maintain it in sealing relation with the appropriate portion of the face.

One technique is the use of adhesives. See for example US Patent Application Publication No. <CIT>. However, the use of adhesives may be uncomfortable for some.

Another technique is the use of one or more straps and/or stabilising harnesses. Many such harnesses suffer from being one or more of ill-fitting, bulky, uncomfortable and awkward to use.

A respiratory pressure therapy (RPT) device may be used individually or as part of a system to deliver one or more of a number of therapies described above, such as by operating the device to generate a flow of air for delivery to an interface to the airways. The flow of air may be pressure-controlled (for respiratory pressure therapies) or flow-controlled (for flow therapies such as HFT). Thus RPT devices may also act as flow therapy devices. Examples of RPT devices include a CPAP device and a ventilator.

An air circuit is a conduit or a tube constructed and arranged to allow, in use, a flow of air to travel between two components of a respiratory therapy system such as the RPT device and the patient interface. In some cases, there may be separate limbs of the air circuit for inhalation and exhalation. In other cases, a single limb air circuit is used for both inhalation and exhalation.

Delivery of a flow of air without humidification may cause drying of airways. The use of a humidifier with an RPT device and the patient interface produces humidified gas that minimizes drying of the nasal mucosa and increases patient airway comfort. In addition, in cooler climates, warm air applied generally to the face area in and about the patient interface is more comfortable than cold air.

Some forms of treatment systems may include a vent to allow the washout of exhaled carbon dioxide. The vent may allow a flow of gas from an interior space of a patient interface, e.g., the plenum chamber, to an exterior of the patient interface, e.g., to ambient.

The present technology is directed towards providing medical devices used in the screening, diagnosis, monitoring, amelioration, treatment, or prevention of respiratory disorders having one or more of improved comfort, cost, efficacy, ease of use and manufacturability.

A first aspect of the present technology relates to apparatus used in the screening, diagnosis, monitoring, amelioration, treatment or prevention of a respiratory disorder.

Another aspect of the present technology relates to methods used in the screening, diagnosis, monitoring, amelioration, treatment or prevention of a respiratory disorder.

An aspect of certain forms of the present technology is to provide methods and/or apparatus that improve the compliance of patients with respiratory therapy.

One form of the present technology comprises a patient interface comprising a seal-forming structure, a plenum chamber, and a positioning and stabilising structure.

One form of the present technology comprises a headgear for use with a patient interface wherein the headgear includes a tension limiting device configured to alert the patient to over tensioning in the headgear.

One form of the present technology comprises a headgear for use with a patient interface wherein the headgear includes a tension control feature configured to limit the amount of tension that a patient applies to the headgear.

One form of the present technology comprises a headgear for use with a patient interface wherein the headgear includes a first position and a second position with a greater length than the first position. Moving from the first position to the second position produces a signal (e.g., an audible sound) observable by the patient (and/or another person).

One form of the present technology comprises a patient interface comprising a seal-forming structure configured to form a seal on the patient's face and a headgear configured to maintain the seal-forming structure in a sealed position, wherein the headgear is configured to output a signal as a result of an overtightened condition.

In some forms, the signal may be auditory, visual, and/or tactile.

One form of the present technology comprises a headgear for a patient interface, the headgear comprising one or more straps each having a first end for connecting to a mask; wherein the first end of each strap comprises, a connection portion, the connection portion being grippable by a user to pull the strap to increase a tension in the strap, a first rigid member, and a second rigid member that extends from a resilient carrier that is connected to the connection portion, the second rigid member being movable relative to the first rigid member when the connection portion is pulled by the user, wherein at least part of the second rigid member is arranged to strike the first rigid member to cause at least an audible alert when the second rigid member travels further than a threshold distance; wherein the resilient carrier is constructed and arranged such that the threshold distance corresponds to a desired tension limit for the strap.

In another form of the present technology, the first rigid member comprises a channel within which the second rigid member is slidingly movable.

In another form of the present technology, the at least part of the second rigid member comprises a projection located at an end of a cantilever arm.

In another form of the present technology, the second rigid member is a C-clip.

In another form of the present technology, the resilient carrier comprises an elastomer.

In another form of the present technology, the resilient carrier is dimensioned to provide the desired tension limit, and/or is formed from a material having a Shore hardness that provides the desired tension limit.

In another form of the present technology, the second rigid member is at least partly embedded in the resilient carrier.

In another form of the present technology, the resilient carrier is connected to the first rigid member via a rigid interface that is separate from the second rigid member.

In another form of the present technology, the rigid interface is embedded in the resilient carrier.

In another form of the present technology, the one or more straps comprise at least one top strap and at least one bottom strap, and wherein a desired tension limit for the at least one top strap is different than a desired tension limit for the at least one bottom strap.

In another form of the present technology, the connection portion is a hook tab.

Another aspect of one form of the present technology is a patient interface that is moulded or otherwise constructed with a perimeter shape which is complementary to that of an intended wearer.

An aspect of one form of the present technology is a method of manufacturing apparatus.

An aspect of certain forms of the present technology is a medical device that is easy to use, e.g. by a person who does not have medical training, by a person who has limited dexterity, vision or by a person with limited experience in using this type of medical device.

An aspect of one form of the present technology is a portable RPT device that may be carried by a person, e.g., around the home of the person.

An aspect of one form of the present technology is a patient interface that may be washed in a home of a patient, e.g., in soapy water, without requiring specialised cleaning equipment. An aspect of one form of the present technology is a humidifier tank that may be washed in a home of a patient, e.g., in soapy water, without requiring specialised cleaning equipment.

The methods, systems, devices and apparatus described may be implemented so as to improve the functionality of a processor, such as a processor of a specific purpose computer, respiratory monitor and/or a respiratory therapy apparatus. Moreover, the described methods, systems, devices and apparatus can provide improvements in the technological field of automated management, monitoring and/or treatment of respiratory conditions, including, for example, sleep disordered breathing.

In one aspect, a method comprises connecting a first rigid member and a second rigid member of a headgear together in order to allow relative movement between the first and second rigid members.

In one aspect, a method comprises cutting a strip of material into a shape of a strap; connecting the strip of material to a first rigid member; connecting a second rigid member to the first rigid member to form a continuous strap; wherein connecting the second rigid member to the first rigid member is configured to allow relative movement between the first and second rigid members.

In some forms, a) the cutting is accomplished using ultrasonic or radio frequency cutting; b) cutting further comprises creating a first portion with a first width and a second portion with a second width smaller than the first width; c) connecting the strip of material to a first rigid member further includes overmolding the first rigid member to the strip of material; d) overmolding occurs on the second width and not on the first width.

In some forms, a) connecting the second rigid member to a resilient carrier; b) the resilient carrier directly connected to the first rigid member and connecting the second rigid member to the first rigid member; c) the resilient carrier includes a base connected to one side of the second rigid member and a tongue connected to the other side of the first rigid member.

<FIG> shows a system including a patient <NUM> wearing a patient interface <NUM>, in the form of a full-face mask, receiving a supply of air at positive pressure from an RPT device <NUM>. Air from the RPT device is humidified in a humidifier <NUM>, and passes along an air circuit <NUM> to the patient <NUM>. The patient is sleeping in a side sleeping position.

<FIG> shows an overview of a human respiratory system including the nasal and oral cavities, the larynx, vocal folds, oesophagus, trachea, bronchus, lung, alveolar sacs, heart and diaphragm.

<FIG> shows a view of a human upper airway including the nasal cavity, nasal bone, lateral nasal cartilage, greater alar cartilage, nostril, lip superior, lip inferior, larynx, hard palate, soft palate, oropharynx, tongue, epiglottis, vocal folds, oesophagus and trachea.

<FIG> is a front view of a face with several features of surface anatomy identified including the lip superior, upper vermilion, lower vermilion, lip inferior, mouth width, endocanthion, a nasal ala, nasolabial sulcus and cheilion. Also indicated are the directions superior, inferior, radially inward and radially outward.

<FIG> is a side view of a head with several features of surface anatomy identified including glabella, sellion, pronasale, subnasale, lip superior, lip inferior, supramenton, nasal ridge, alar crest point, otobasion superior and otobasion inferior. Also indicated are the directions superior & inferior, and anterior & posterior.

<FIG> is a further side view of a head. The approximate locations of the Frankfort horizontal and nasolabial angle are indicated. The coronal plane is also indicated.

<FIG> shows a base view of a nose with several features identified including naso-labial sulcus, lip inferior, upper Vermilion, naris, subnasale, columella, pronasale, the major axis of a naris and the midsagittal plane.

<FIG> shows a side view of the superficial features of a nose.

<FIG> shows subcutaneal structures of the nose, including lateral cartilage, septum cartilage, greater alar cartilage, lesser alar cartilage, sesamoid cartilage, nasal bone, epidermis, adipose tissue, frontal process of the maxilla and fibrofatty tissue.

<FIG> shows a medial dissection of a nose, approximately several millimeters from the midsagittal plane, amongst other things showing the septum cartilage and medial crus of greater alar cartilage.

<FIG> shows a front view of the bones of a skull including the frontal, nasal and zygomatic bones. Nasal concha are indicated, as are the maxilla, and mandible.

<FIG> shows a lateral view of a skull with the outline of the surface of a head, as well as several muscles. The following bones are shown: frontal, sphenoid, nasal, zygomatic, maxilla, mandible, parietal, temporal and occipital. The mental protuberance is indicated. The following muscles are shown: digastricus, masseter, sternocleidomastoid and trapezius.

<FIG> shows an anterolateral view of a nose.

<FIG> shows a patient interface in the form of a nasal mask in accordance with one form of the present technology.

<FIG> shows a schematic of a cross-section through a structure at a point. An outward normal at the point is indicated. The curvature at the point has a positive sign, and a relatively large magnitude when compared to the magnitude of the curvature shown in <FIG>.

<FIG> shows a schematic of a cross-section through a structure at a point. An outward normal at the point is indicated. The curvature at the point has a positive sign, and a relatively small magnitude when compared to the magnitude of the curvature shown in <FIG>.

<FIG> shows a schematic of a cross-section through a structure at a point. An outward normal at the point is indicated. The curvature at the point has a value of zero.

<FIG> shows a schematic of a cross-section through a structure at a point. An outward normal at the point is indicated. The curvature at the point has a negative sign, and a relatively small magnitude when compared to the magnitude of the curvature shown in <FIG>.

<FIG> shows a schematic of a cross-section through a structure at a point. An outward normal at the point is indicated. The curvature at the point has a negative sign, and a relatively large magnitude when compared to the magnitude of the curvature shown in <FIG>.

<FIG> shows a cushion for a mask that includes two pillows. An exterior surface of the cushion is indicated. An edge of the surface is indicated. Dome and saddle regions are indicated.

<FIG> shows a cushion for a mask. An exterior surface of the cushion is indicated. An edge of the surface is indicated. A path on the surface between points A and B is indicated. A straight line distance between A and B is indicated. Two saddle regions and a dome region are indicated.

<FIG> shows the surface of a structure, with a one dimensional hole in the surface. The illustrated plane curve forms the boundary of a one dimensional hole.

<FIG> shows a cross-section through the structure of <FIG>. The illustrated surface bounds a two dimensional hole in the structure of <FIG>.

<FIG> shows a perspective view of the structure of <FIG>, including the two dimensional hole and the one dimensional hole. Also shown is the surface that bounds a two dimensional hole in the structure of <FIG>.

<FIG> shows a mask having an inflatable bladder as a cushion.

<FIG> shows a cross-section through the mask of <FIG>, and shows the interior surface of the bladder. The interior surface bounds the two dimensional hole in the mask.

<FIG> shows a further cross-section through the mask of <FIG>. The interior surface is also indicated.

<FIG> shows a left ear, including the left ear helix.

<FIG> shows a right ear, including the right ear helix.

<FIG> shows a view of a mask, including the sign of the torsion of the space curve defined by the edge of the sealing membrane in different regions of the mask.

<FIG> shows a view of a plenum chamber <NUM> showing a sagittal plane and a mid-contact plane.

<FIG> shows a view of a posterior of the plenum chamber of <FIG>. The direction of the view is normal to the mid-contact plane. The sagittal plane in <FIG> bisects the plenum chamber into left-hand and right-hand sides.

<FIG> shows a cross-section through the plenum chamber of <FIG>, the cross-section being taken at the sagittal plane shown in <FIG>. A 'mid-contact' plane is shown. The mid-contact plane is perpendicular to the sagittal plane. The orientation of the mid-contact plane corresponds to the orientation of a chord <NUM> which lies on the sagittal plane and just touches the cushion of the plenum chamber at two points on the sagittal plane: a superior point <NUM> and an inferior point <NUM>. Depending on the geometry of the cushion in this region, the mid-contact plane may be a tangent at both the superior and inferior points.

<FIG> shows the plenum chamber <NUM> of <FIG> in position for use on a face. The sagittal plane of the plenum chamber <NUM> generally coincides with the midsagittal plane of the face when the plenum chamber is in position for use. The mid-contact plane corresponds generally to the `plane of the face' when the plenum chamber is in position for use. In <FIG> the plenum chamber <NUM> is that of a nasal mask, and the superior point <NUM> sits approximately on the sellion, while the inferior point <NUM> sits on the lip superior.

<FIG> shows headgear in accordance with one form of the present technology, in flattened form.

<FIG> shows a schematic view of an end portion of a strap of the headgear of <FIG>.

<FIG> is a schematic series of views showing operation of a tension limit detection feature of the strap of <FIG>.

<FIG> is an enlarged view of a protrusion of the strap of <FIG>.

<FIG> is a schematic view showing the elastic deformation of the strap of <FIG>.

<FIG> show various stages of manufacture of a headgear strap in accordance with one form of the present technology.

<FIG> show various forms of patient interface for which headgear straps having a tension limit detection feature are suitable.

The following description is provided in relation to various examples which may share one or more common characteristics and/or features.

In one form, the present technology comprises a method for treating a respiratory disorder comprising applying positive pressure to the entrance of the airways of a patient <NUM>.

In one form, the present technology comprises a respiratory therapy system for treating a respiratory disorder. The respiratory therapy system may comprise an RPT device <NUM> for supplying a flow of air to the patient <NUM> via an air circuit <NUM> and a patient interface <NUM>.

A non-invasive patient interface <NUM> in accordance with one aspect of the present technology comprises the following functional aspects: a seal-forming structure <NUM>, a plenum chamber <NUM>, a positioning and stabilising structure (also referred to herein as headgear) <NUM>, a vent <NUM>, one form of connection port <NUM> for connection to air circuit <NUM>, and a forehead support <NUM>. In some forms a functional aspect may be provided by one or more physical components. In some forms, one physical component may provide one or more functional aspects. In use the seal-forming structure <NUM> is arranged to surround an entrance to the airways of the patient so as to maintain positive pressure at the entrance(s) to the airways of the patient <NUM>. The sealed patient interface <NUM> is therefore suitable for delivery of positive pressure therapy.

If a patient interface is unable to comfortably deliver a minimum level of positive pressure to the airways, the patient interface may be unsuitable for respiratory pressure therapy.

The patient interface <NUM> in accordance with one form of the present technology is constructed and arranged to be able to provide a supply of air at a positive pressure of at least <NUM> cmH<NUM>O with respect to ambient.

In one form of the present technology, a seal-forming structure <NUM> provides a target seal-forming region, and may additionally provide a cushioning function. The target seal-forming region is a region on the seal-forming structure <NUM> where sealing may occur. The region where sealing actually occurs- the actual sealing surface- may change within a given treatment session, from day to day, and from patient to patient, depending on a range of factors including for example, where the patient interface was placed on the face, tension in the positioning and stabilising structure and the shape of a patient's face.

In one form the target seal-forming region is located on an outside surface of the seal-forming structure <NUM>.

In certain forms of the present technology, the seal-forming structure <NUM> is constructed from a biocompatible material, e.g. silicone rubber.

A seal-forming structure <NUM> in accordance with the present technology may be constructed from a soft, flexible, resilient material such as silicone.

In certain forms of the present technology, a system is provided comprising more than one a seal-forming structure <NUM>, each being configured to correspond to a different size and/or shape range. For example the system may comprise one form of a seal-forming structure <NUM> suitable for a large sized head, but not a small sized head and another suitable for a small sized head, but not a large sized head.

In one form, the seal-forming structure includes a sealing flange utilizing a pressure assisted sealing mechanism. In use, the sealing flange can readily respond to a system positive pressure in the interior of the plenum chamber <NUM> acting on its underside to urge it into tight sealing engagement with the face. The pressure assisted mechanism may act in conjunction with elastic tension in the positioning and stabilising structure.

In one form, the seal-forming structure <NUM> comprises a sealing flange and a support flange. The sealing flange comprises a relatively thin member with a thickness of less than about <NUM>, for example about <NUM> to about <NUM>, which extends around the perimeter of the plenum chamber <NUM>. Support flange may be relatively thicker than the sealing flange. The support flange is disposed between the sealing flange and the marginal edge of the plenum chamber <NUM>, and extends at least part of the way around the perimeter. The support flange is or includes a spring-like element and functions to support the sealing flange from buckling in use.

In one form, the seal-forming structure may comprise a compression sealing portion or a gasket sealing portion. In use the compression sealing portion, or the gasket sealing portion is constructed and arranged to be in compression, e.g. as a result of elastic tension in the positioning and stabilising structure.

In one form, the seal-forming structure comprises a tension portion. In use, the tension portion is held in tension, e.g. by adjacent regions of the sealing flange.

In one form, the seal-forming structure comprises a region having a tacky or adhesive surface.

In certain forms of the present technology, a seal-forming structure may comprise one or more of a pressure-assisted sealing flange, a compression sealing portion, a gasket sealing portion, a tension portion, and a portion having a tacky or adhesive surface.

In one form, the non-invasive patient interface <NUM> comprises a seal-forming structure that forms a seal in use on a nose bridge region or on a nose-ridge region of the patient's face.

In one form, the seal-forming structure includes a saddle-shaped region constructed to form a seal in use on a nose bridge region or on a nose-ridge region of the patient's face.

In one form, the non-invasive patient interface <NUM> comprises a seal-forming structure that forms a seal in use on an upper lip region (that is, the lip superior) of the patient's face.

In one form, the seal-forming structure includes a saddle-shaped region constructed to form a seal in use on an upper lip region of the patient's face.

In one form the non-invasive patient interface <NUM> comprises a seal-forming structure that forms a seal in use on a chin-region of the patient's face.

In one form, the seal-forming structure includes a saddle-shaped region constructed to form a seal in use on a chin-region of the patient's face.

In one form, the seal-forming structure that forms a seal in use on a forehead region of the patient's face. In such a form, the plenum chamber may cover the eyes in use.

In one form the seal-forming structure of the non-invasive patient interface <NUM> comprises a pair of nasal puffs, or nasal pillows, each nasal puff or nasal pillow being constructed and arranged to form a seal with a respective naris of the nose of a patient.

Nasal pillows in accordance with an aspect of the present technology include: a frusto-cone, at least a portion of which forms a seal on an underside of the patient's nose, a stalk, a flexible region on the underside of the frusto-cone and connecting the frusto-cone to the stalk. In addition, the structure to which the nasal pillow of the present technology is connected includes a flexible region adjacent the base of the stalk. The flexible regions can act in concert to facilitate a universal joint structure that is accommodating of relative movement both displacement and angular of the frusto-cone and the structure to which the nasal pillow is connected. For example, the frusto-cone may be axially displaced towards the structure to which the stalk is connected.

The plenum chamber <NUM> has a perimeter that is shaped to be complementary to the surface contour of the face of an average person in the region where a seal will form in use. In use, a marginal edge of the plenum chamber <NUM> is positioned in close proximity to an adjacent surface of the face. Actual contact with the face is provided by the seal-forming structure <NUM>. The seal-forming structure <NUM> may extend in use about the entire perimeter of the plenum chamber <NUM>. In some forms, the plenum chamber <NUM> and the seal-forming structure <NUM> are formed from a single homogeneous piece of material.

In certain forms of the present technology, the plenum chamber <NUM> does not cover the eyes of the patient in use. In other words, the eyes are outside the pressurised volume defined by the plenum chamber. Such forms tend to be less obtrusive and / or more comfortable for the wearer, which can improve compliance with therapy.

In certain forms of the present technology, the plenum chamber <NUM> is constructed from a transparent material, e.g. a transparent polycarbonate. The use of a transparent material can reduce the obtrusiveness of the patient interface, and help improve compliance with therapy. The use of a transparent material can aid a clinician to observe how the patient interface is located and functioning.

In certain forms of the present technology, the plenum chamber <NUM> is constructed from a translucent material. The use of a translucent material can reduce the obtrusiveness of the patient interface, and help improve compliance with therapy.

The seal-forming structure <NUM> of the patient interface <NUM> of the present technology may be held in sealing position in use by the positioning and stabilising structure (headgear) <NUM>.

In one form the positioning and stabilising structure <NUM> provides a retention force at least sufficient to overcome the effect of the positive pressure in the plenum chamber <NUM> to lift off the face.

In one form the positioning and stabilising structure <NUM> provides a retention force to overcome the effect of the gravitational force on the patient interface <NUM>.

In one form the positioning and stabilising structure <NUM> provides a retention force as a safety margin to overcome the potential effect of disrupting forces on the patient interface <NUM>, such as from tube drag, or accidental interference with the patient interface.

In one form of the present technology, a positioning and stabilising structure <NUM> is provided that is configured in a manner consistent with being worn by a patient while sleeping. In one example the positioning and stabilising structure <NUM> has a low profile, or cross-sectional thickness, to reduce the perceived or actual bulk of the apparatus. In one example, the positioning and stabilising structure <NUM> comprises at least one strap having a rectangular cross-section. In one example the positioning and stabilising structure <NUM> comprises at least one flat strap.

In one form of the present technology, a positioning and stabilising structure <NUM> is provided that is configured so as not to be too large and bulky to prevent the patient from lying in a supine sleeping position with a back region of the patient's head on a pillow.

In one form of the present technology, a positioning and stabilising structure <NUM> is provided that is configured so as not to be too large and bulky to prevent the patient from lying in a side sleeping position with a side region of the patient's head on a pillow.

In one form of the present technology, a positioning and stabilising structure <NUM> is provided with a decoupling portion located between an anterior portion of the positioning and stabilising structure <NUM>, and a posterior portion of the positioning and stabilising structure <NUM>. The decoupling portion does not resist compression and may be, e.g. a flexible or floppy strap. The decoupling portion is constructed and arranged so that when the patient lies with their head on a pillow, the presence of the decoupling portion prevents a force on the posterior portion from being transmitted along the positioning and stabilising structure <NUM> and disrupting the seal.

In one form of the present technology, a positioning and stabilising structure <NUM> comprises a strap constructed from a laminate of a fabric patient-contacting layer, a foam inner layer and a fabric outer layer. In one form, the foam is porous to allow moisture, (e.g., sweat), to pass through the strap. In one form, the fabric outer layer comprises loop material to engage with a hook material portion.

In certain forms of the present technology, a positioning and stabilising structure <NUM> comprises a strap that is extensible, e.g. resiliently extensible. For example the strap may be configured in use to be in tension, and to direct a force to draw a seal-forming structure into sealing contact with a portion of a patient's face. In an example the strap may be configured as a tie.

In one form of the present technology, the positioning and stabilising structure comprises a first tie, the first tie being constructed and arranged so that in use at least a portion of an inferior edge thereof passes superior to an otobasion superior of the patient's head and overlays a portion of a parietal bone without overlaying the occipital bone.

In one form of the present technology suitable for a nasal-only mask or for a full-face mask, the positioning and stabilising structure includes a second tie, the second tie being constructed and arranged so that in use at least a portion of a superior edge thereof passes inferior to an otobasion inferior of the patient's head and overlays or lies inferior to the occipital bone of the patient's head.

In one form of the present technology suitable for a nasal-only mask or for a full-face mask, the positioning and stabilising structure includes a third tie that is constructed and arranged to interconnect the first tie and the second tie to reduce a tendency of the first tie and the second tie to move apart from one another.

In certain forms of the present technology, a positioning and stabilising structure <NUM> comprises a strap that is bendable and e.g. non-rigid. An advantage of this aspect is that the strap is more comfortable for a patient to lie upon while the patient is sleeping.

In certain forms of the present technology, a positioning and stabilising structure <NUM> comprises a strap constructed to be breathable to allow moisture vapour to be transmitted through the strap,
In certain forms of the present technology, a system is provided comprising more than one positioning and stabilizing structure <NUM>, each being configured to provide a retaining force to correspond to a different size and/or shape range. For example the system may comprise one form of positioning and stabilizing structure <NUM> suitable for a large sized head, but not a small sized head, and another. suitable for a small sized head, but not a large sized head.

<FIG> shows an example of headgear <NUM>, which may, for example, be used as part of the patient interface <NUM> of <FIG>. The headgear <NUM> may be one example of the positioning and stablising structure. The headgear <NUM> may be constructed from a composite of textile material, polyurethane foam, and/or loop material and hook material, and the headgear <NUM> may include a pair of upper straps <NUM> and lower straps <NUM> and a generally triangular back portion <NUM>. In the illustrated example, the triangular back portion <NUM> may be an opening formed between several straps of the headgear <NUM>, although the triangular back portion <NUM> may also include complete material coverage (e.g., so that the patient's head is not exposed through the triangular back portion <NUM> while in use). The back portion <NUM> may also be another shape (e.g., circular, elliptical, rectangular, etc.) instead of triangular. A piece of hook material <NUM> (e.g., such as Velcro®), also referred to herein as a hook tab, is attached to the end of each of the four straps so that the straps may be secured to and/or through attachment points on the mask <NUM>, or to another structure that supports the mask <NUM> (see <FIG>).

The hook material <NUM> may be `one way' hook material so that it does not catch on itself in the process of overlaying the straps before they are brought into engagement.

In other, unillustrated, arrangements, the straps <NUM>, <NUM> may be adapted to fit to a male clip connector which clips into a female connector moulded into a mask frame of mask <NUM>. In other, unillustrated examples, the connection portion of each strap <NUM>, <NUM> may include one of a male and female connector for connecting to a cooperating female or male connector on the mask <NUM>. The male or female connector on the straps <NUM>, <NUM> may be used in place of the hook material <NUM>, or in addition to the hook material <NUM>. In still further unillustrated examples, the connection portion of each strap <NUM>, <NUM> may include a magnet for connecting to a separate magnet on the mask and/or on another portion of the respective strap <NUM>, <NUM>. In a still further unillustrated embodiment, the connection portion of each strap <NUM>, <NUM> may include both a magnet and a mechanical fastener.

Each of the straps <NUM>, <NUM> may comprise a main portion formed from a fabric/foam/fabric laminate, and a first end (respectively, <NUM> for the upper straps <NUM> and <NUM> for the lower straps <NUM>) for connecting to the mask <NUM> (e.g., either directly or via an intermediate structure, like a frame).

Straps <NUM>, <NUM> of headgear <NUM> may each comprise a tension limit detection feature. The feature may indicate when a predetermined tension limit in the straps <NUM>, <NUM> has been exceeded. This feature may be a visual indicator, an auditory indicator, and/or a tactile indicator that may alert the patient and/or others that the headgear <NUM> is too tight. The patient may then loosen the headgear <NUM> and/or choose a different sized headgear <NUM>.

As best shown in <FIG>, an end portion <NUM> of each of the upper straps <NUM> comprises a connection portion, in the form of hook tab <NUM>, that may be gripped by a user to pull the strap <NUM> to tighten (e.g., to increase tension in) the strap. The end portion <NUM> comprises a first rigid member <NUM> and a second rigid member (formed by <NUM>, <NUM>, <NUM>) that extends from a resilient carrier (<NUM>, <NUM>) that is connected to the hook tab <NUM>.

In the illustrated form of the technology, the second rigid member is a C-clip structure that comprises a pair of cantilever arms <NUM> joined by a web <NUM>. The second rigid member may be at least partly embedded in the resilient carrier. For example, at least the web <NUM> may be embedded in the resilient carrier with the cantilever arms <NUM> being exposed.

As illustrated in <FIG> (as well as <FIG>), the web <NUM> may be connected between the base <NUM> and the tongue <NUM> that make up the resilient carrier <NUM>, <NUM>. This connection may be that the web <NUM>, and the resilient carrier <NUM>, <NUM> are integrally formed. The web <NUM> may extend so that it is longer than at least a portion of the width of the resilient carrier <NUM>, <NUM>. For example, the web <NUM> may be longer than at least a portion of the width of the tongue <NUM>. The cantilever arms <NUM> may extend from the ends of the web <NUM> and be spaced apart from the resilient carrier <NUM>, <NUM>.

In some forms, the cantilever arms <NUM> and the web <NUM> may be formed as an integral piece. Although in other forms, each cantilever arm <NUM> may be separately connected to the web <NUM>.

The second rigid member <NUM>, <NUM> is movable relative to the first rigid member <NUM> when the hook tab <NUM> is pulled by the user. That is, the second rigid member <NUM>, <NUM> is pulled away from the first rigid member <NUM> when the hook tab <NUM> is pulled as shown in <FIG>. At least part of the second rigid member <NUM>, <NUM> is arranged to strike (or contact) the first rigid member <NUM> to cause at least an audible alert when the second rigid member <NUM>, <NUM> travels further than a threshold distance. For example, the second rigid member <NUM>, <NUM> may have a first position that is less than the threshold distance and a second position that is greater than the threshold distance. Moving from the first position to the second position outputs a signal, in this case the audible alert, that is perceived by the patient or another person.

In the example of <FIG>, the at least part of the second rigid member <NUM>, <NUM> that is arranged to contact the first rigid member <NUM> is a protrusion <NUM> located at an end of the cantilever arm <NUM>. Depending on the corresponding engagement means, the protrusions <NUM> may be outwardly facing (as shown in <FIG>) or inwardly facing. As the hook tab <NUM> is pulled, this causes tension to be applied to the resilient carrier <NUM>, <NUM>, which in turn causes the cantilever arms <NUM> to move in the direction of pulling. As described in more detail below, this tension may result in relative movement between the extension portion <NUM> and the connector portion <NUM> of the resilient carrier <NUM>, <NUM>. This results in the protrusions <NUM> of the cantilever arms <NUM> to engage with one or more protrusions or projections <NUM> of the first rigid member <NUM> such that the protrusions <NUM> ride over the protrusions or projections <NUM> and the cantilever arm <NUM> is deflected. Eventually, once the cantilever arms <NUM> travel a threshold distance, the cantilever arms <NUM> snap back and strike the surface of the first rigid member <NUM> to cause an audible alert to the user that a tension limit has been reached, to thus prevent over-tightening of the strap <NUM>.

The protrusions <NUM> are sized such that when they snap back and strike the surface of the first rigid member <NUM>, an audible sound is produced. For example, as the protrusion <NUM> rides over the projection <NUM>, the cantilever <NUM> and protrusion <NUM> are pushed into a deflected position. The protrusion <NUM> moves resiliently and/or elastically into the deflected position. As the protrusion rides past the projection <NUM>, it is released from the deflected position into a relaxed position, the movement of which causes the cantilever <NUM> to strike the surface of the projection <NUM> to produce the audible sound. The intensity of the audible sound may, for example, be dependent on the distance travelled by the cantilever and/or protrusion between the deflected position and the relaxed position. This in turn may be dependent on the height <NUM> of the protrusion <NUM> relative to the cantilever <NUM>. In some forms, the height <NUM> may be about <NUM> to about <NUM>. In some forms, the height <NUM> may be about <NUM> to about <NUM>. In some forms, the height <NUM> may be about <NUM> to about <NUM>. A greater height allows for a substantial snapping back of the cantilever arm <NUM> such that the striking of the cantilever arm <NUM> onto the projection <NUM> is substantial enough to produce an audible sound. The inner end <NUM> of the protrusion <NUM> may also have a sloping face <NUM>, with a gradient of about <NUM>° to about <NUM>°. In some forms, the gradient may be about <NUM>° to about <NUM>°. In some forms, the gradient may be about <NUM>° to about <NUM>°, preferably about <NUM>°. This facilitates the release of the second rigid member <NUM> from the first rigid member <NUM>.

The rigidity of the second rigid member <NUM>, <NUM> is constructed and arranged such that the striking of the surface of the first rigid member <NUM> may cause an audible alert. Striking the surface of the first rigid member <NUM> may also cause a tactile alert, particularly if the patient is wearing the headgear <NUM> when the striking occurs. For example, the vibrations that contribute to the audible alert may also be felt by the patient, which could provide a benefit for hearing-impaired patients. In particular, the degree to which the second rigid member <NUM>, <NUM> may resiliently flex may be provided by a Young's modulus value. This may be obtained from a slope of a linear elastic region of a stress-strain curve, where Hooke's law is generally obeyed. Another way may be to characterise the second rigid member <NUM>, <NUM> by its yield strength, the point where a material begins to deform plastically. Any material which allows the second rigid member <NUM>, <NUM> to resiliently flex may be used.

The resilient carrier <NUM>, <NUM> is constructed and arranged such that the threshold distance corresponds to a desired tension limit for the strap. In particular, the degree to which the resilient carrier <NUM>, <NUM> may be stretched, and thus the maximum distance that the second rigid member <NUM>, <NUM> may travel, may be controlled by the dimensions (e.g. the thickness) and/or the Shore hardness (equivalently, flexural modulus) of the resilient carrier <NUM>, <NUM>.

The tension limit may be controlled via several factors. These factors, such as surface area, force applied, the corresponding Young's modulus (may be derived from Shore Hardness) of the choice of material and the initial length of the resilient carrier <NUM> may influence the stretch of the resilient carrier <NUM>, <NUM> when tension is applied to the headgear (such as, when the hook tab <NUM> is pulled). The resilient carrier <NUM> may be deformed by a measurement given by a total elastic deformation. The total elastic deformation of the resilient carrier <NUM> (dltotal) is the sum of the horizontal elastic deformation <NUM> (dlhorizontal) and the perpendicular elastic deformation 3378A, 3378B (dlperpendicular), as represented by the formula below: <MAT>.

The first rigid member <NUM> may comprise a channel <NUM> within which the second rigid member <NUM>, <NUM> is slidingly movable. The channel <NUM> may have sidewalls from which extend projections <NUM> that are arranged to engage with the protrusions <NUM> of the cantilever arms <NUM> to cause the cantilever arms <NUM> to deflect inwardly (towards the centre of the channel <NUM>), as shown in the middle panel of <FIG>.

As shown in <FIG>, the projections <NUM> of the first rigid member <NUM> are located at the end of the first rigid member <NUM>, such that once the threshold distance is reached, the protrusions <NUM> of the cantilever arms <NUM> protrude beyond the end of the first rigid member <NUM>. This provides a visual indication that the tension limit has been exceeded, in addition to the audible alert caused by the snapping motion of the C-clip <NUM> as the protrusions <NUM> travel over the projections <NUM>. It will be appreciated, though, that other configurations are possible. For example, projections <NUM> may be located at intermediate locations of the sidewalls of the channel <NUM>. Additionally, the visual indication could also include an alternate color being exposed as a result of the cantilever arms protruding beyond the end of the first rigid member <NUM>.

In another variant, which is not shown, projections <NUM> need not be located on the sidewalls of the channel <NUM>, but may be located within the channel <NUM> itself. In this variant, the protrusions <NUM> of the cantilever arms <NUM> do not face towards the sidewalls, but instead face towards a centre of the channel <NUM>, such that they deflect outwardly (i.e., away from the centre and towards the sidewalls) when the hook tab <NUM> is pulled.

The resilient carrier <NUM>, <NUM> may comprise a connector portion <NUM> that is used to couple the resilient carrier to the first rigid member <NUM>. For example, the connector portion <NUM> may comprise an embedded rigid connector <NUM> (which is separate from second rigid member <NUM>, <NUM>) and may have an aperture that is shaped such that the connector portion <NUM> may be fitted over a boss <NUM> located in the channel <NUM> of the first rigid member <NUM>. The boss <NUM> may have a substantially rectangular surface. In some forms, the width of the boss <NUM> may be variable. For example, some examples of the boss <NUM> may include a wider portion distal to the opening of the channel <NUM> (i.e., proximate to the projections <NUM>). The resilient carrier may also comprise an extension portion <NUM>, for example in the form of a tongue as shown in <FIG>, that carries the C-clip <NUM>, <NUM>. The extension portion <NUM> may be movable relative to the connector portion <NUM>. For example, engagement between the boss <NUM> and the connector portion <NUM> may fix the connector portion and a tensile force applied to the hook tab <NUM> may move the extension portion <NUM> relative to the connector portion <NUM>.

In some forms, the boss <NUM> may extend from the surface of the channel <NUM>. The boss <NUM> may not extend beyond the top of the channel <NUM> so that the height of the boss <NUM> (e.g., the distance from the surface of the channel <NUM> to the top of the boss <NUM>) is not wider than the first rigid member <NUM>, although in other examples the height of the boss <NUM> may extend beyond the width of the first rigid member <NUM>.

The provision of the resilient carrier allows for at least a partial decoupling of a pulling force exerted by the user. When the hook material <NUM> is pulled, the pulling force is transmitted to the second rigid member <NUM>, <NUM> such that the protrusion <NUM> on the second rigid member engages the projection <NUM> on the first rigid member when a minimum amount of force is exerted (for example when the retention force reaches about <NUM> N). Further pulling force exerted on the hook material <NUM> is transmitted and dissipated by the resilient carrier due to its elasticity and/or toughness (e.g., when the pulling force exceeds about <NUM> N). This prevents the user from overtightening the strap while also provides a larger range of the pulling force.

The end portions <NUM> of the lower straps <NUM> may be constructed substantially identically to the end portions <NUM> of upper straps <NUM>. In some forms of the present technology, it may be desirable to have a different tension limit for the upper straps <NUM> than the lower straps <NUM>. If so, the resilient carrier <NUM>, <NUM> of the upper and lower straps <NUM>, <NUM> may be constructed in a manner that provides different tension limits.

The hook material <NUM> and first rigid member <NUM> may be made of any suitable polymer. The elasticity and/or rigidity of the polymer should be sufficient for the second rigid member <NUM>, <NUM> to ride over the first rigid member <NUM> when the hook material <NUM> is pulled. The second rigid member <NUM>, <NUM> may be made of any suitable polymer such as polyethylene, polypropylene, polyurethane or polyethylene terephthalate (PET). Advantageously, the suitable polymer is resiliently flexible and sufficiently tough. The resilient carrier <NUM>, <NUM> may be made from a silicone based material or elastomer. Examples of elastomers include, but is not limited to, polyisoprene, polybutadiene, chloroprene rubber, polychloroprene, Neoprene, Baypren, butyl rubber, styrene-butadiene rubber, nitrile rubber, ethylene propylene rubber, epichlorohydrin rubber, polyacrylic rubber, silicone rubber, fluorosilicone rubber, fluoroelastomers, polyether block amides, chlorosulfonated polyethylene, and ethylene-vinyl acetate.

Turning now to <FIG>, an exemplary method of manufacturing a headgear strap <NUM> will be described.

In a first step, as illustrated schematically in <FIG>, a strip of material may be cut into a desired shape by any suitable means, such as by an ultrasonic or radio frequency cutting device. The illustrated shape may comprise a linear portion 3320a and a tongue 3320b extending from and having a smaller width than the linear portion 3320a, although any other shape may be used.

Next, as shown in <FIG>, an insert molding process may be used to attach the first rigid member <NUM> to the strip of material, such that the first rigid member <NUM> is overmoulded on the tongue 3320b. As shown in <FIG>, the tongue 3320b may be completely covered as a result of the molding process.

Separately, as shown in <FIG>, the second rigid member <NUM>, <NUM>, resilient carrier <NUM>, <NUM>, and hook tab <NUM> may be assembled together. The base <NUM> is insert-moulded over the rigid connector <NUM>, and the tongue <NUM> is insert-moulded at one end over the C-clip <NUM>, <NUM> and at the other end over an end of the hook tab <NUM>. The base <NUM> may similarly be insert-moulded to the second rigid member <NUM>, <NUM> (although other means of connection, like an interlock method, may be used). When insert moulding the base <NUM>, an aperture <NUM> is formed that extends through the rigid connector <NUM>.

Finally, as shown in <FIG>, the strap <NUM> may be assembled by fitting the base <NUM>/rigid connector <NUM> over the boss <NUM> of channel <NUM> in the first rigid member <NUM>. For example, the aperture <NUM> may be aligned with the boss <NUM> so that the boss <NUM> may be received through the aperture <NUM>.

As described above, certain forms of the boss <NUM> may have a variable width, specifically with a wider portion distal to the channel. The aperture <NUM> may be slightly smaller than the widest portion of the boss <NUM>. As part of assembling the rigid connector <NUM> to the first rigid member <NUM>, the rigid connector <NUM> may snap to the first rigid member <NUM> as a result of the smaller aperture <NUM> passing around the larger boss <NUM>. This may result in a snap-fit connector that secures the first rigid member <NUM> and the rigid connector <NUM> together. In some forms, the rigid connector <NUM> and the first rigid member <NUM> may be removable from one another.

Straps <NUM> or <NUM> having a tension limit detection feature have been described above with reference to the headgear <NUM> shown in <FIG> and <FIG>. However, it will be appreciated that the same principles may be applied to straps of a wide variety of other headgear, such as headgear with both upper and lower straps of various kinds as shown in <FIG> and <FIG>, or headgear with only a single strap as shown in <FIG>. It will be appreciated that the strap tension suitable for retention of the mask in a therapeutically effective position will vary in these different patient interfaces, and that the properties of the resilient carrier of the strap may be varied accordingly to provide the appropriate tension limit detection.

In one form, the patient interface <NUM> includes a vent <NUM> constructed and arranged to allow for the washout of exhaled gases, e.g. carbon dioxide.

In certain forms the vent <NUM> is configured to allow a continuous vent flow from an interior of the plenum chamber <NUM> to ambient whilst the pressure within the plenum chamber is positive with respect to ambient. The vent <NUM> is configured such that the vent flow rate has a magnitude sufficient to reduce rebreathing of exhaled CO2 by the patient while maintaining the therapeutic pressure in the plenum chamber in use.

One form of vent <NUM> in accordance with the present technology comprises a plurality of holes, for example, about <NUM> to about <NUM> holes, or about <NUM> to about <NUM> holes, or about <NUM> to about <NUM> holes.

The vent <NUM> may be located in the plenum chamber <NUM>. Alternatively, the vent <NUM> is located in a decoupling structure, e.g., a swivel.

In one form the patient interface <NUM> includes at least one decoupling structure, for example, a swivel or a ball and socket.

Connection port <NUM> allows for connection to the air circuit <NUM>.

In one form, the patient interface <NUM> includes a forehead support <NUM>.

In one form, the patient interface <NUM> includes an anti-asphyxia valve.

In one form of the present technology, a patient interface <NUM> includes one or more ports that allow access to the volume within the plenum chamber <NUM>. In one form this allows a clinician to supply supplementary oxygen. In one form, this allows for the direct measurement of a property of gases within the plenum chamber <NUM>, such as the pressure.

An RPT device <NUM> in accordance with one aspect of the present technology comprises mechanical, pneumatic, and/or electrical components and is configured to execute one or more algorithms for application of respiratory therapy. The RPT device <NUM> may be configured to generate a flow of air for delivery to a patient's airways, such as to treat one or more of the respiratory conditions described elsewhere in the present document.

An air circuit <NUM> in accordance with an aspect of the present technology is a conduit or a tube constructed and arranged to allow, in use, a flow of air to travel between two components such as RPT device <NUM> and the patient interface <NUM>.

Headgear for a patient interface, the headgear comprising: one or more straps each having a first end for connecting to a mask; wherein the first end of at least one of the one or more straps comprises: a connection portion, the connection portion being grippable by a user to pull the strap to increase a tension in the strap; a first rigid member; and a second rigid member that extends from a resilient carrier that is connected to the connection portion, the second rigid member being movable relative to the first rigid member when the connection portion is pulled by the user, wherein at least part of the second rigid member is arranged to strike the first rigid member to cause at least an audible alert when the second rigid member travels further than a threshold distance; wherein the resilient carrier is constructed and arranged such that the threshold distance corresponds to a desired tension limit for the strap.

Headgear according to aspect A1, wherein the first rigid member comprises a channel within which the second rigid member is slidingly movable.

Headgear according to aspect A2, wherein the at least part of the second rigid member comprises a projection located at an end of a cantilever arm.

Headgear according to aspect A3, wherein the second rigid member is a C-clip.

Headgear according to any one of aspects A1 to A4, wherein the desired tension limit is about <NUM> N, and wherein the resilient carrier comprises an elastomer configured to facilitate elastic deformation relative to the first rigid member.

Headgear according to any one of aspects A1 to A5, wherein the resilient carrier is dimensioned to provide the desired tension limit, and/or is formed from a material having a Shore hardness that provides the desired tension limit.

Headgear according to any one of aspects A1 to A6, wherein the second rigid member is at least partly embedded in the resilient carrier.

Headgear according to any one of aspects A1 to A7, wherein the resilient carrier is connected to the first rigid member via a rigid interface that is separate from the second rigid member.

Headgear according to aspect A8, wherein the rigid interface is embedded in the resilient carrier.

Headgear according to any one of aspects A1 to A9, wherein the one or more straps comprise at least one top strap and at least one bottom strap, and wherein a tension limit for the at least one top strap is different than a tension limit for the at least one bottom strap.

Headgear according to any one of aspects A1 to A10, wherein the connection portion is a hook tab.

Headgear according to any one of aspects A1 to A11, wherein the first rigid member includes a channel with a boss extending from a surface of the channel, and wherein the second rigid member includes an aperture, the second rigid member being receivable within the channel and the boss being receivable within the aperture.

Headgear according to aspect A12, wherein the boss is removably receivable within the aperture.

Headgear according to any one of aspects A1 to A13, wherein the second rigid member is movable between a deflected position and a relaxed position, and wherein when the second rigid member travels further than the threshold distance, the second rigid member moves from the deflected position to the relaxed position.

Headgear according to any one of aspects A1 to A14, wherein the second rigid member includes at least one protrusion and the first rigid member includes at least one projection, wherein contact between the at least one protrusion and the at least one projection is configured to cause the second rigid member to deflect.

Headgear for a patient interface, the headgear comprising: one or more straps each having a first end for connecting to a mask; wherein the first end of at least one of the one or more straps comprises: a connection portion, the connection portion being grippable by a user to pull the strap to increase a tension in the strap; a first rigid member; and a second rigid member that extends from a resilient carrier that is connected to the connection portion, the second rigid member being movable relative to the first rigid member when the connection portion is pulled by the user, wherein at least part of the second rigid member is arranged to strike the first rigid member to cause at least an audible alert when the second rigid member travels further than a threshold distance; wherein the resilient carrier is constructed and arranged such that the threshold distance corresponds to a desired tension limit for the strap.

Headgear according to aspect B1, wherein the first rigid member comprises a channel within which the second rigid member is slidingly movable.

Headgear according to aspect B2, wherein the at least part of the second rigid member comprises a projection located at an end of a cantilever arm.

Headgear according to aspect B3, wherein the second rigid member is a C-clip.

Headgear according to aspect B1, wherein the desired tension limit is about <NUM> N, and wherein the resilient carrier comprises an elastomer configured to facilitate elastic deformation relative to the first rigid member.

Headgear according to aspect B1, wherein the resilient carrier is dimensioned to provide the desired tension limit, and/or is formed from a material having a Shore hardness that provides the desired tension limit.

Headgear according to aspect B1, wherein the second rigid member is at least partly embedded in the resilient carrier.

Headgear according to aspect B1, wherein the resilient carrier is connected to the first rigid member via a rigid interface that is separate from the second rigid member.

Headgear according to aspect B8, wherein the rigid interface is embedded in the resilient carrier.

Headgear according to aspect B1, wherein the one or more straps comprise at least one top strap and at least one bottom strap, and wherein a tension limit for the at least one top strap is different than a tension limit for the at least one bottom strap.

Headgear according to aspect B1, wherein the connection portion is a hook tab.

Headgear according to aspect B1, wherein the first rigid member includes a channel with a boss extending from a surface of the channel, and wherein the second rigid member includes an aperture, the second rigid member being receivable within the channel and the boss being receivable within the aperture.

Headgear according to aspect B12, wherein the boss is removably receivable within the aperture.

Headgear according to aspect B1, wherein the second rigid member is movable between a deflected position and a relaxed position, and wherein when the second rigid member travels further than the threshold distance, the second rigid member moves from the deflected position to the relaxed position.

Headgear according to aspect B1, wherein the second rigid member includes at least one protrusion and the first rigid member includes at least one projection, wherein contact between the at least one protrusion and the at least one projection is configured to cause the second rigid member to deflect.

Headgear according to aspect B15, wherein the protrusion has a height of about <NUM> to about <NUM>.

Headgear according to aspect B <NUM>, wherein: the second rigid member is a C-clip and is at least partly embedded in the resilient carrier; and the resilient carrier is connected to the first rigid member via a rigid interface that is separate from the second rigid member.

Headgear according to aspect B1, wherein: the one or more straps comprise at least one top strap and at least one bottom strap, and wherein a tension limit for the at least one top strap is different than a tension limit for the at least one bottom strap; the resilient carrier comprises an elastomer configured to facilitate elastic deformation relative to the first rigid member; and the connection portion is a hook tab.

Headgear according to aspect B1, wherein: the first rigid member includes a channel with a boss extending from a surface of the channel, and the first rigid member includes at least one projection; the second rigid member is a C-clip and includes a pair of cantilever arms, the at least part of the second rigid member comprises a projection located at least one of the pair of cantilever arms; the second rigid member further includes an aperture, the second rigid member being receivable within the channel and the boss being receivable within the aperture; and the second rigid member further includes at least one protrusion, wherein contact between the at least one protrusion and the at least one projection is configured to cause the second rigid member to deflect.

The headgear of aspect B1, wherein the first rigid member comprises a channel within which the second rigid member is slidingly movable; the resilient carrier is connected to the first rigid member via a rigid interface that is separate from the second rigid member; the second rigid member is movable between a deflected position and a relaxed position, and wherein when the second rigid member travels further than the threshold distance, the second rigid member moves from the deflected position to the relaxed position; and the second rigid member includes at least one protrusion and the first rigid member includes at least one projection, wherein contact between the at least one protrusion and the at least one projection is configured to cause the second rigid member to deflect.

Headgear for a patient interface, the headgear comprising: one or more straps each having a first end for connecting to a mask; wherein the first end of each strap comprises: a second rigid member that is connected to the connection portion, the second rigid member being movable relative to the first rigid member when the connection portion is pulled by the user, wherein at least part of the second rigid member is arranged to output an alert when the second rigid member travels further than a threshold distance, and wherein the second rigid member is movable between a deflected position and a relaxed position, and wherein when the second rigid member travels further than the threshold distance, the second rigid member moves from the deflected position to the relaxed position.

Headgear for the patient interface of aspect C1, wherein the second rigid member extends from a resilient carrier that is connected to the connection portion; and wherein the resilient carrier is constructed and arranged such that the threshold distance corresponds to a desired tension limit for the strap.

Headgear according to aspect C2, wherein the second rigid member is at least partly embedded in the resilient carrier.

Headgear according to any one of aspects C2 to C3, wherein the resilient carrier is connected to the first rigid member via a rigid interface that is separate from the second rigid member.

Headgear according to aspect C4, wherein the rigid interface is embedded in the resilient carrier.

Headgear according to any one of aspects C1 to C5, wherein the first rigid member comprises a channel within which the second rigid member is slidingly movable.

Headgear according to any one of aspects C1 to C6, wherein the at least part of the second rigid member comprises a projection located at an end of a cantilever arm.

Headgear according to any one of aspects C1 to C7, wherein the second rigid member is a C-clip.

Headgear according to any one of aspects C1 to C8, wherein the one or more straps comprise at least one top strap and at least one bottom strap, and wherein a desired tension limit for the at least one top strap is different than a desired tension limit for the at least one bottom strap.

Headgear according to any one of aspects C1 to C9, wherein the connection portion is a hook tab.

Headgear according to any one of aspects C1 to C10, wherein the first rigid member includes a channel with a boss extending from a surface of the channel, and wherein the second rigid member includes an aperture, the second rigid member being receivable within the channel and the boss being receivable within the aperture.

Headgear according to aspect C11, wherein the boss is removably receivable within the aperture.

Headgear according to any one of aspects C1 to C12, wherein the second rigid member is movable between a deflected position and a relaxed position, and wherein when the second rigid member travels further than the threshold distance, the second rigid member moves from the deflected position to the relaxed position.

Headgear according to any one of aspects C1 to C13, wherein the second rigid member includes at least one protrusion and the first rigid member includes at least one projection, wherein contact between the at least one protrusion and the at least one projection is configured to cause the second rigid member to deflect.

Air: In certain forms of the present technology, air may be taken to mean atmospheric air, and in other forms of the present technology air may be taken to mean some other combination of breathable gases, e.g. oxygen enriched air.

Ambient: In certain forms of the present technology, the term ambient will be taken to mean (i) external of the treatment system or patient, and (ii) immediately surrounding the treatment system or patient.

For example, ambient humidity with respect to a humidifier may be the humidity of air immediately surrounding the humidifier, e.g. the humidity in the room where a patient is sleeping. Such ambient humidity may be different to the humidity outside the room where a patient is sleeping.

In another example, ambient pressure may be the pressure immediately surrounding or external to the body.

In certain forms, ambient (e.g., acoustic) noise may be considered to be the background noise level in the room where a patient is located, other than for example, noise generated by an RPT device or emanating from a mask or patient interface. Ambient noise may be generated by sources outside the room.

Automatic Positive Airway Pressure (APAP) therapy: CPAP therapy in which the treatment pressure is automatically adjustable, e.g. from breath to breath, between minimum and maximum limits, depending on the presence or absence of indications of SDB events.

Continuous Positive Airway Pressure (CPAP) therapy: Respiratory pressure therapy in which the treatment pressure is approximately constant through a respiratory cycle of a patient. In some forms, the pressure at the entrance to the airways will be slightly higher during exhalation, and slightly lower during inhalation. In some forms, the pressure will vary between different respiratory cycles of the patient, for example, being increased in response to detection of indications of partial upper airway obstruction, and decreased in the absence of indications of partial upper airway obstruction.

Flow rate: The volume (or mass) of air delivered per unit time. Flow rate may refer to an instantaneous quantity. In some cases, a reference to flow rate will be a reference to a scalar quantity, namely a quantity having magnitude only. In other cases, a reference to flow rate will be a reference to a vector quantity, namely a quantity having both magnitude and direction. Flow rate may be given the symbol Q. `Flow rate' is sometimes shortened to simply 'flow' or 'airflow'.

In the example of patient respiration, a flow rate may be nominally positive for the inspiratory portion of a breathing cycle of a patient, and hence negative for the expiratory portion of the breathing cycle of a patient. Device flow rate, Qd, is the flow rate of air leaving the RPT device. Total flow rate, Qt, is the flow rate of air and any supplementary gas reaching the patient interface via the air circuit. Vent flow rate, Qv, is the flow rate of air leaving a vent to allow washout of exhaled gases. Leak flow rate, Ql, is the flow rate of leak from a patient interface system or elsewhere. Respiratory flow rate, Qr, is the flow rate of air that is received into the patient's respiratory system.

Flow therapy: Respiratory therapy comprising the delivery of a flow of air to an entrance to the airways at a controlled flow rate referred to as the treatment flow rate that is typically positive throughout the patient's breathing cycle.

Humidifier: The word humidifier will be taken to mean a humidifying apparatus constructed and arranged, or configured with a physical structure to be capable of providing a therapeutically beneficial amount of water (H<NUM>O) vapour to a flow of air to ameliorate a medical respiratory condition of a patient.

Leak: The word leak will be taken to be an unintended flow of air. In one example, leak may occur as the result of an incomplete seal between a mask and a patient's face. In another example leak may occur in a swivel elbow to the ambient.

Noise, conducted (acoustic): Conducted noise in the present document refers to noise which is carried to the patient by the pneumatic path, such as the air circuit and the patient interface as well as the air therein. In one form, conducted noise may be quantified by measuring sound pressure levels at the end of an air circuit.

Noise, radiated (acoustic): Radiated noise in the present document refers to noise which is carried to the patient by the ambient air. In one form, radiated noise may be quantified by measuring sound power/pressure levels of the object in question according to ISO <NUM>.

Noise, vent (acoustic): Vent noise in the present document refers to noise which is generated by the flow of air through any vents such as vent holes of the patient interface.

Oxygen enriched air: Air with a concentration of oxygen greater than that of atmospheric air (<NUM>%), for example at least about <NUM>% oxygen, at least about <NUM>% oxygen, at least about <NUM>% oxygen, at least about <NUM>% oxygen, at least about <NUM>% oxygen, at least about <NUM>% oxygen, at least about <NUM>% oxygen, or at least about <NUM>% oxygen. "Oxygen enriched air" is sometimes shortened to "oxygen".

Medical Oxygen: Medical oxygen is defined as oxygen enriched air with an oxygen concentration of <NUM>% or greater.

Patient: A person, whether or not they are suffering from a respiratory condition.

Pressure: Force per unit area. Pressure may be expressed in a range of units, including cmHzO, g-f/cm<NUM> and hectopascal. <NUM> cmH<NUM>O is equal to <NUM>-f/cm<NUM> and is approximately <NUM> hectopascal (<NUM> hectopascal = <NUM> Pa = <NUM> N/m<NUM> = <NUM> millibar ~ <NUM> atm). In this specification, unless otherwise stated, pressure is given in units of cmHzO.

The pressure in the patient interface is given the symbol Pm, while the treatment pressure, which represents a target value to be achieved by the interface pressure Pm at the current instant of time, is given the symbol Pt.

Respiratory Pressure Therapy: The application of a supply of air to an entrance to the airways at a treatment pressure that is typically positive with respect to atmosphere.

Ventilator: A mechanical device that provides pressure support to a patient to perform some or all of the work of breathing.

Silicone or Silicone Elastomer: A synthetic rubber. In this specification, a reference to silicone is a reference to liquid silicone rubber (LSR) or a compression moulded silicone rubber (CMSR). One form of commercially available LSR is SILASTIC (included in the range of products sold under this trademark), manufactured by Dow Corning. Another manufacturer of LSR is Wacker. Unless otherwise specified to the contrary, an exemplary form of LSR has a Shore A (or Type A) indentation hardness in the range of about <NUM> to about <NUM> as measured using ASTM D2240.

Polycarbonate: a thermoplastic polymer of Bisphenol-A Carbonate.

Textile: A flexible material formed from a network of fibres, which may be natural, artificial, or a combination thereof. The fibres (e.g. wool, flax, cotton, hemp, and/or artificial fibres) may be spun into a yarn that is woven, knitted, crocheted, knotted, tatted, felted, and/or braided to form the textile. As used herein, the terms "textile" and "fabric" are interchangeable.

Resilience: Ability of a material to absorb energy when deformed elastically and to release the energy upon unloading.

Resilient: Will release substantially all of the energy when unloaded. Includes e.g. certain silicones, and thermoplastic elastomers.

Hardness: The ability of a material per se to resist deformation (e.g. described by a Young's Modulus, or an indentation hardness scale measured on a standardised sample size).

Stiffness (or rigidity) of a structure or component: The ability of the structure or component to resist deformation in response to an applied load. The load may be a force or a moment, e.g. compression, tension, bending or torsion. The structure or component may offer different resistances in different directions. The inverse of stiffness is flexibility.

Floppy structure or component: A structure or component that will change shape, e.g. bend, when caused to support its own weight, within a relatively short period of time such as <NUM> second.

Rigid structure or component: A structure or component that will not substantially change shape when subject to the loads typically encountered in use. An example of such a use may be setting up and maintaining a patient interface in sealing relationship with an entrance to a patient's airways, e.g. at a load of approximately <NUM> to <NUM> cmH<NUM>O pressure.

As an example, an I-beam may comprise a different bending stiffness (resistance to a bending load) in a first direction in comparison to a second, orthogonal direction. In another example, a structure or component may be floppy in a first direction and rigid in a second direction.

Anti-asphyxia valve (AAV): The component or sub-assembly of a mask system that, by opening to atmosphere in a failsafe manner, reduces the risk of excessive CO2 rebreathing by a patient.

Elbow: An elbow is an example of a structure that directs an axis of flow of air travelling therethrough to change direction through an angle. In one form, the angle may be approximately <NUM> degrees. In another form, the angle may be more, or less than <NUM> degrees. The elbow may have an approximately circular cross-section. In another form the elbow may have an oval or a rectangular cross-section. In certain forms an elbow may be rotatable with respect to a mating component, e.g. about <NUM> degrees. In certain forms an elbow may be removable from a mating component, e.g. via a snap connection. In certain forms, an elbow may be assembled to a mating component via a one-time snap during manufacture, but not removable by a patient.

Frame: Frame will be taken to mean a mask structure that bears the load of tension between two or more points of connection with a headgear. A mask frame may be a non-airtight load bearing structure in the mask. However, some forms of mask frame may also be air-tight.

Headgear: Headgear will be taken to mean a form of positioning and stabilizing structure designed for use on a head. For example the headgear may comprise a collection of one or more struts, ties and stiffeners configured to locate and retain a patient interface in position on a patient's face for delivery of respiratory therapy. Some ties are formed of a soft, flexible, elastic material such as a laminated composite of foam and fabric.

Membrane: Membrane will be taken to mean a typically thin element that has, preferably, substantially no resistance to bending, but has resistance to being stretched.

Plenum chamber: a mask plenum chamber will be taken to mean a portion of a patient interface having walls at least partially enclosing a volume of space, the volume having air therein pressurised above atmospheric pressure in use. A shell may form part of the walls of a mask plenum chamber.

Seal: May be a noun form ("a seal") which refers to a structure, or a verb form ("to seal") which refers to the effect. Two elements may be constructed and/or arranged to 'seal' or to effect 'sealing' therebetween without requiring a separate 'seal' element per se.

Shell: A shell will be taken to mean a curved, relatively thin structure having bending, tensile and compressive stiffness. For example, a curved structural wall of a mask may be a shell. In some forms, a shell may be faceted. In some forms a shell may be airtight. In some forms a shell may not be airtight.

Stiffener: A stiffener will be taken to mean a structural component designed to increase the bending resistance of another component in at least one direction.

Strut: A strut will be taken to be a structural component designed to increase the compression resistance of another component in at least one direction.

Swivel (noun): A subassembly of components configured to rotate about a common axis, preferably independently, preferably under low torque. In one form, the swivel may be constructed to rotate through an angle of at least <NUM> degrees. In another form, the swivel may be constructed to rotate through an angle less than <NUM> degrees. When used in the context of an air delivery conduit, the sub-assembly of components preferably comprises a matched pair of cylindrical conduits. There may be little or no leak flow of air from the swivel in use.

Tie (noun): A structure designed to resist tension.

Vent: (noun): A structure that allows a flow of air from an interior of the mask, or conduit, to ambient air for clinically effective washout of exhaled gases. For example, a clinically effective washout may involve a flow rate of about <NUM> litres per minute to about <NUM> litres per minute, depending on the mask design and treatment pressure.

All publications mentioned herein disclose and describe the methods and/or materials which are the subject of those publications. The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present technology is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates, which may need to be independently confirmed.

The terms "comprises" and "comprising" should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced.

Although the technology herein has been described with reference to particular examples, it is to be understood that these examples are merely illustrative of the principles and applications of the technology. In some instances, the terminology and symbols may imply specific details that are not required to practice the technology. For example, although the terms "first" and "second" may be used, unless otherwise specified, they are not intended to indicate any order but may be utilised to distinguish between distinct elements. Furthermore, although process steps in the methodologies may be described or illustrated in an order, such an ordering is not required. Those skilled in the art will recognize that such ordering may be modified and/or aspects thereof may be conducted concurrently or even synchronously.

Claim 1:
Headgear for a patient interface (<NUM>), the headgear (<NUM>) comprising:
one or more straps (<NUM>, <NUM>) each having a first end for connecting to a mask (<NUM>);
wherein the first end of at least one of the one or more straps (<NUM>, <NUM>) comprises:
a connection portion, the connection portion being grippable by a user to pull the strap (<NUM>, <NUM>) to increase a tension in the strap (<NUM>, <NUM>);
a first rigid member (<NUM>); and
a second rigid member (<NUM>, <NUM>, <NUM>) that extends from a resilient carrier (<NUM>, <NUM>) that is connected to the connection portion, the second rigid member (<NUM>, <NUM>, <NUM>) being movable relative to the first rigid member (<NUM>) when the connection portion is pulled by the user, wherein at least part of the second rigid member (<NUM>, <NUM>, <NUM>) is arranged to strike the first rigid member (<NUM>) to cause at least an audible alert when the second rigid member travels further than a threshold distance;
wherein the resilient carrier (<NUM>, <NUM>) is constructed and arranged such that the threshold distance corresponds to a desired tension limit for the strap (<NUM>, <NUM>),
wherein the first rigid member (<NUM>) includes a channel (<NUM>) with a boss (<NUM>) extending from a surface of the channel (<NUM>), and wherein the second rigid member includes an aperture (<NUM>), the second rigid member (<NUM>, <NUM>, <NUM>) being receivable within the channel (<NUM>) and the boss (<NUM>) being receivable within the aperture (<NUM>), and
wherein the second rigid member (<NUM>, <NUM>, <NUM>) includes at least one protrusion (<NUM>) and the first rigid member (<NUM>) includes at least one projection (<NUM>), wherein contact between the at least one protrusion (<NUM>) and the at least one projection (<NUM>) is configured to cause the second rigid member (<NUM>, <NUM>, <NUM>) to deflect.