Abstract:
A valved nasal cannula adapted to provide a positive pressure in the airway using the breathing of the intended user as a source of positive pressure without the need for an external source of energy and/or compressed air. The cannula is designed so as to be relatively easily insertable and retractable into and from the nasal vestibule portion of the nose of the intended user without requiring manual dexterity.

Description:
[0001]    This application is a continuation of U.S. Ser. No. 12/301,157, filed Mar. 16, 2009, which was the National Stage of International Application PCT/CA2007/000922, filed May 18, 2007. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to the general field of devices and methods for breathing problems such as snoring and sleep apnea and is particularly concerned with a valved nasal cannula. 
       BACKGROUND OF THE INVENTION 
       [0003]    The prevalence of breathing disorders during sleep, including snoring and sleep apnea, is relatively high. Such disorders are associated with significant morbidity. 
         [0004]    The harsh and rough sound known as snoring is typically caused when a person breathes through his or her mouth during sleep in such a manner so as to cause the soft palate and/or uvula to vibrate, but may also occur when the person breathes through his or her nose. In addition to the irritating snoring sound which may cause potential marital stress, it has been suggested that mouth breathing is unhealthy. Indeed, it contributes to the development of gum diseases such as pyorrhoea and also to an unpleasant dry mouth syndrome. 
         [0005]    Sleep apnea is a potentially lethal condition characterized by multiple mixed or obstructed apneas during sleep. Symptoms of sleep apnea include repetitive episodes of inordinately loud snoring and excessive daytime sleepiness. 
         [0006]    The characteristic snoring pattern noted during sleep apnea is one in which inspiratory snores gradually increase when obstruction of the upper airway develops. A loud, choking inspiratory gasp then occurs as the respiratory efforts succeed in overcoming the occlusion. 
         [0007]    The aroused individual subject to sleep apnea is usually aware of neither the breathing difficulty nor of the accompanying body movements that, at times, violently disturb his or her sleep. Typically, a diagnostic study is necessary for an adequate description of the problematic sleep breathing pattern. 
         [0008]    Apneic episodes during sleep are typically defined as cessations of air flow at nose and mouth lasting  10  seconds or more. It can be readily documented by so-called poly-somnographic recordings. 
         [0009]    There are varying degrees of apnea differentiated by the frequency of periodic breathing cessation episodes during sleep, and also the degree of hypoxia resulting from the related irregular breathing pattern. 
         [0010]    When normal breathing is disrupted during sleep, an increased carbon dioxide level and a reduced oxygen level appear in the blood. The sleeping person is then suddenly aroused and gasps for air. This gasping for air is often accompanied by a loud snort. 
         [0011]    An increased carbon dioxide level in the blood can cause adverse effects on the vital organs. The heart is usually caused to pump harder and at a higher rate in an effort to compensate for the lack of oxygen. Other organs, such as the kidneys and liver are suddenly confronted with increased blood flow and must adjust to cope with this change. This cycle may be repeated many times during a night&#39;s rest and often results in a general lack of proper rest and the restorative benefits thereof. 
         [0012]    Some of the health related problems associated with sleep apnea include hypertension, stroke, irregular heartbeat, heart attack as well as the psychogenic conditions from the loss of restful sleep. 
         [0013]    It is generally believed that the cause to this condition is a narrowing of the airways while sleeping. This is believed to be caused by a collapse of the tissue structures surrounding the airway. There seems, however, to be no consensus as to what tissue structures the condition should be-attributed to and as to why certain tissue structures close. 
         [0014]    There are differing locations and patterns of pharyngeal collapse for each person. In addition to the physical findings and properties which characterize the pharynx in individuals with obstructive sleep apnea such as increased collapsibility, increase compliance, increased resistance and decreased cross-sectional area, the physical properties and spatial relationships of the pharyngeal airway, head and neck, as well as the neuromuscular integrity of the airway and a mechanism of breathing control must also be considered relevant in their contribution to the mechanism and precipitation of upper airway collapse. 
         [0015]    In general, it may be considered that obstructive apnea occurs during sleep when the pharyngeal dilator muscle activity (genioglossus, the infrahyoid muscle and the palatal muscle group) that normally maintain airway potency during inspiration through dilation of the airways, is diminished. When the intraluminal negative pressure of the airway reaches a critical point, the combination of redundant tissues and the loss of pharyngeal muscle tonus cause airway collapse during inspiration. It should, however, be noted that obstruction has also been found to occur during expiration and inspiration. 
         [0016]    The prior art is replete with various methods and devices that have been proposed in attempts to cure snoring and sleep apnea. Treatments available for sleep apnea vary from weight loss to surgical interventions to prosthetic devices. Although weight loss is the most desirable approach, few patients are able to comply with their diets and very few can afford to continue the exposure to the symptoms of sleep apnea for extended periods while losing sufficient weight to reduce or cure the disease. 
         [0017]    Surgical approaches are only effective in about 50% of cases. They are also invasive, expensive and may produce undesirable side effects. 
         [0018]    The most successful prosthetic device has been the nasal continuous positive airway ventilator or pressure known as “CPAP”. The advantages of the nasal CPAP system are that it produces immediate relief, is non-invasive and can be used while achieving weight loss, hence eliminating the need for surgery. 
         [0019]    The CPAP technique, however, suffers from some important drawbacks. One of the primary drawbacks associated with nasal CPAP has been compliance. While nearly all patients are fitted with nasal CPAP as an initial treatment modality, many cease using the system after a few months. At least three primary factors have been identified as the cause for poor compliance amongst individuals using the CPAP system. One such factor is the lack of perfect fit and discomfort of wearing a nasal mask. The positive pressure of the ventilator flow is often mentioned as another factor. Some patients experience an uncomfortable and annoying sensation of forced air stream in their nose and mouth. Also, dry mouth and throat are often cited as the source of dissatisfaction with the sleep apnea ventilators known as CPAP. 
         [0020]    Another type of devices used for treating sleep apnea is a valved nasal cannula insertable in the nostril of an intended user. Such cannulae typically include a body defining a passageway. A valve extends across the passageway and is configured to allow air to flow substantially unaffected into the nose of the intended user, but to restrict any outgoing flow of air so as to provide a backpressure, with the intention of keeping the airways open so as to reduce snoring. 
         [0021]    Many such devices have a valve taking the form of a flexible leaflet extending across the passageway and attached to the body at the periphery thereof. This is the case, for example, of some of the nasal cannulae described in U.S. Pat. No. 6,626,179 issued Sep. 30, 2003 to Pedley, and of some of the cannula described in US Patent Application 2006/0150979 of Doshi et al. published Jul. 13, 2006. However, such leaflets may be influenced by gravity as the orientation of the leaflet relatively to its attachment point will influence its dynamic properties. Furthermore, these leaflets present a relatively large lever relatively to their attachment points and therefore have a relatively large response time when transitioning between their “free flowing” configurations to their “backpressure providing” configurations. 
         [0022]    The above-referenced US Patent Application 2006/0150979 presents some valved nasal cannulae that alleviate at least in part these problems by having valves that are supported at the center thereof by a frame extending across the passageway. Also, some of the valves presented in this document are supported by the body of the cannula at two diametrically opposed location and fold in two to let air flow upon inspiration by the intended user. These two types of valves however may lead to the valve leaflet sticking to itself or to the relatively flat surfaces of the valve support, which again reduces response time and may even lead to valve malfunction. 
         [0023]    Another problem of these valves resides in that if the valve becomes detached from the body of the cannula for any reason, the valve may be aspirated by the user of the valve and block the airways of this user. 
         [0024]    Accordingly, there exists a need in the industry for an improved valved nasal cannula. An object of the present invention is therefore to provide an improved valved nasal cannula. 
       SUMMARY OF THE INVENTION 
       [0025]    In a first aspect, a valved nasal cannula is insertable in a nose of an intended user and usable to selectively restrict a flow of air flowing through the valved nasal cannula, the nose having a nostril defining a nostril inlet and a nostril vestibule extending inwardly into the nose from the nostril inlet, the valved nasal cannula including:
       a cannula body, the cannula body defining a cannula passageway extending therethrough, the cannula passageway defining a passageway longitudinal axis, the cannula body also defining a cannula proximal end and a substantially longitudinally opposed cannula distal end, the cannula body being, at least in part, insertable in the nostril with the cannula proximal end positioned inside the nostril vestibule substantially spaced apart from the nostril inlet and the cannula distal end positioned substantially adjacent the nostril inlet;   a valve operatively coupled to the cannula body for selectively restricting the flow of air through the cannula passageway; and   a protective grid, the protective grid extending from the cannula body across said cannula passageway, the protective grid being located closer to the cannula proximal end than the valve;   whereby the protective grid increases the safety of the valved nasal cannula by preventing relatively large objects from being inhaled by the intended user while the valved nasal cannula is inserted in the nostril.       
 
         [0030]    Advantages of the present embodiment may include that the proposed valved nasal cannula is adapted to provide a positive pressure in the airway using the breathing of the intended user as a source of positive pressure without the need for an external source of energy and/or compressed air. The proposed cannula is designed so as to be relatively easily insertable and retractable into and from the nasal vestibule portion of the nose of the intended user without requiring manual dexterity. 
         [0031]    The protective grid serves, among other purposes, to prevent the valve from obstructing the airways of the intended user should the valve become detached from the cannula body. 
         [0032]    Also, the proposed cannula is designed so as to be comfortable once inserted into the nasal vestibule of the intended user. The proposed cannula is designed so as to be substantially fittingly inserted into the nasal vestibule and, in at least some embodiments, to enlarge the latter so as to optimize the breathing passageway. 
         [0033]    Also, in some embodiments of the invention, the proposed cannula is designed so as to be resiliently deformable in order to reduce the risk of injury should the nose of the intended wearer be subjected to an impact while housing the proposed cannula. 
         [0034]    The proposed cannula may be used for reducing sleep disorder breathing and/or as a breathing exercise as it may be the case for example in Chronic Obstructive Pulmonary Disease (COPD) affecting the inspiratory muscles. In order to exercise the muscles for such a disease (COPD) the cannula is inserted, for a short period of exercise, upside down into the nasal nostril or preferably a special cannula having a reverse configuration would be used. This configuration allows to induce a resistance to air flow during the inspiration phase rather than at the expiration phase consequently the inspiratory muscles will gain in strength. 
         [0035]    The proposed cannula may optionally be provided with features such as thermal insulation properties in order to reduce the thermal exchange between the airway and the air flowing therethrough, filtering and/or air moisturizing means, active substance dispensing means for dispensing active substances having a stimulating, therapeutic and/or prophylactic effect. 
         [0036]    The proposed device is also designed so as to be manufacturable using conventional forms of manufacturing and conventional materials such as a polymeric resin injecting moulding process using suitable hypo-allergic resins so as to provide a nasal cannula that will be economically feasible, long-lasting and relatively trouble-free in operation. 
         [0037]    The proposed nasal cannula is also designed so as to optimize the air flow therethrough. 
         [0038]    The proposed nasal cannula is also designed so as to reduce the resistance to air flow during the inspiratory phase of breathing and so as to be substantially silent during use. 
         [0039]    Other objects, advantages and features of the various embodiments will become more apparent upon reading of the following non-restrictive description of preferred embodiments thereof, given by way of example only with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0040]    In the appended drawings: 
           [0041]      FIG. 1 , in a partial elevational view, illustrates a valved nasal cannula in accordance with an embodiment of the present invention, the nasal cannula being shown inserted into the nasal vestibule region of the nose of an intended user, the intended user being shown, in part, in phantom lines; 
           [0042]      FIG. 2 , in a partial perspective view with sections taken out, illustrates a valved nasal cannula in accordance with an embodiment of the present invention; 
           [0043]      FIG. 3 , in a longitudinal cross-sectional view, illustrates some of the features of a valved nasal cannula in accordance with an embodiment of the present invention, the valved nasal cannula being shown with its valve in an opened configuration; 
           [0044]      FIG. 4 , in a partial longitudinal cross-sectional view with sections taken out, illustrates part of a valved nasal cannula in accordance with an embodiment of the present invention, the nasal cannula being shown with its valve in an opened configuration; 
           [0045]      FIG. 5 , in a partially exploded perspective view, illustrates a valved nasal cannula in accordance with an embodiment of the present invention; 
           [0046]      FIG. 6 , in a perspective view, illustrates the valved nasal cannula shown in  FIG. 5 ; 
           [0047]      FIG. 7 , in a top view, illustrates a valved nasal cannula in accordance with another embodiment of the present invention. 
           [0048]      FIG. 8 , in a partially exploded perspective view, illustrates a valved nasal cannula in accordance with yet another embodiment of the present invention; and 
           [0049]      FIG. 9 , in a perspective view, illustrates the valved nasal cannula having a prehensile protrusion. 
       
    
    
     DETAILED DESCRIPTION 
       [0050]    Referring to  FIG. 1 , there is shown a valved nasal cannula in accordance with an embodiment of the present invention generally indicated by the reference numeral  10 . The nasal cannula  10  is shown inserted in the nostril  12  of an intended user  14  substantially in register with the nasal vestibule  16  of the intended user  14 . The valved nasal cannula  10  is insertable in the nose of the intended user  14  and usable to selectively restrict a flow of air flowing through the valved nasal cannula  10 . The nostril  12  defines a nostril inlet  15  and a nostril vestibule, part of the nasal vestibule  16 , the nostril vestibule extending inwardly into the nose from the nostril inlet  15 . 
         [0051]    As illustrated more specifically in  FIG. 2 , the nasal cannula  10  has a cannula body generally indicated by the reference numeral  18 . The cannula body  18  defines a cannula passageway  20  extending therethrough along a passageway longitudinal axis  22 . 
         [0052]    The cannula body  18  also defines a body inner surface  24  and an opposed body outer surface  26 . The cannula body  18  is configured and sized for being substantially snugly fitted in the region of the nasal vestibule  16 . The internal tissue of the nasal vestibule  16  is typically considered to be less sensitive to tactile stimulation than downstream nasal tissue and, hence, less susceptible of sending nociceptive signals to the brain upon a foreign body being inserted therein. 
         [0053]    The cannula body  18  typically has a substantially frusto-conical configuration defining a cannula proximal end  28  and a longitudinally opposed cannula distal end  30 . The cannula body  18  is, at least in part, insertable in the nostril  12  with the cannula proximal end  28  positioned inside the nostril vestibule substantially spaced apart from the nostril inlet  15  and the cannula distal end  30  positioned substantially adjacent the nostril inlet  15 . In other words, the cannula proximal end  28  is adapted to be positioned nearer to the sinuses of the intended wearer while the cannula distal end  30  is adapted to be positioned nearer to the inlet of the nostril  12 . Typically, the external diameter of the cannula proximal end  28  is smaller than that of the cannula distal end  30 . Therefore, in these embodiments, the body outer surface  26  is tapered in a direction leading from the cannula distal end  30  towards the cannula proximal end  28 . 
         [0054]    As illustrated more specifically in  FIG. 3 , the cannula outer surface  26  is angled relative to the passageway longitudinal axis  22  by an outer surface-to-longitudinal axis angle  32 . Throughout the Figures, the outer surface-to-longitudinal axis angle  32  is shown having a substantially constant value of a few degrees. It should, however, be understood that the outer surface-to-longitudinal axis angle  32  could vary without departing from the scope of the present invention. Typically, the cannula body  18  is configured and sized for providing a radial outward pressure so as to slightly increase the size of the nasal vestibule  16 . 
         [0055]    The outer surface-to-longitudinal axis angle  32 , as well as the diameter of the cannula body  18  and its length are typically chosen for a given user in order to ensure a comfortable yet substantially snug fit in the nasal vestibule  16  of the intended user in order to ensure that the cannula body  18  remains in proper alignment therewith. 
         [0056]    The substantially frustro-conical configuration of the body outer surface  26  allows for such a comfortable yet snug fit taking into consideration the anatomical configuration of the internal surface of the nasal vestibule  16  since it substantially increases the probability of having a substantially uniform or constant contact with the internal surface of the nasal vestibule  16 . 
         [0057]    In order to reduce the risks of creating a localized pressure onto the relatively sensitive tissues of the nasal cavity, the body outer surface  26  is typically provided with a substantially smooth texture. Also, the body outer surface  26  is typically provided with a substantially resiliently deformable characteristic. The cannula body  18  may be made out of an integral material having such characteristics or, alternatively, the body outer surface  26  may be coated with a substantially resiliently deformable material. 
         [0058]    Typically, the cannula body  18 , has a whole, is made out of a substantially resiliently deformable material and provides resiliency so as to be able to temporarily deform upon an impact of a predetermined magnitude being imparted thereon so as to reduce the risk of injury to the internal tissues of the nose of the intended user  14  should an impact be imparted externally on the nose of the intended user  14 . More specifically, the cannula body  18  is substantially resiliently deformable between a body undeformed configuration and a body deformed configuration, whereby the cannula body  18  is able to temporarily deform from the body undeformed configuration to the body deformed configuration upon an impact of the predetermined magnitude being imparted thereon 
         [0059]    In at least one embodiment of the invention, the cannula body  18  is made out first of a resiliently deformable material while the body outer surface  26  is coated with a second resiliently deformable material. The characteristics of the first and second resiliently deformable materials may be identical or different without departing from the scope of the present invention. 
         [0060]    In some embodiments of the invention, the cannula body  18  and/or the coating on the body external surface  26  is made of an hypo-allergic material such as a latex-free polymeric resin so as to reduce the risk of creating an allergic reaction once inserted into the nose of the intended user. 
         [0061]    Also, in at least some embodiments of the invention, the cannula body  18  and/or the coating on the body external surface  26  is made out of a heat insulating material so as to reduce the heat transfer between the mucosa of the nose of the intended user and the air flowing through the nasal cannula. The reduced heat transfer may allow for cooler air to reach internal tissues so as to reduce oedema thereof. 
         [0062]    The nasal cannula  10  further includes a valve for selectively restricting the flow of air through the cannula passageway  20 . The valve is operatively coupled to the cannula body for selectively restricting the flow of air through the cannula passageway. Typically, the valve is a diaphragm-type valve and is positioned in the cannula passageway  20  substantially spaced apart from both the cannula proximal and distal ends  28  and  30 , although other types and positions of the valve could be used without departing from the scope of the present invention. 
         [0063]    In the embodiments shown throughout the drawings, and as seen for example in  FIGS. 3 and 4 , the valve includes a diaphragm disc  34  made out of a resiliently deformable material. The diaphragm disc  34  is mounted on a diaphragm frame generally indicated by the reference numeral  36  for extending across the cannula passageway  20 . 
         [0064]    As illustrated more specifically in  FIG. 5 , the diaphragm frame  36  includes at least one and preferably an array of supporting ribs or spokes  38  extending across the cannula passageway  20 . Typically, the spokes  38  extend substantially radially from a substantially centrally disposed hub  40  to the body inner surface  24 , and therefore extend substantially diametrically across the cannula passageway  20 . 
         [0065]    As illustrated more specifically in  FIG. 4 , the hub  40  typically includes an anchoring portion for anchoring a central portion of the diaphragm disc  34 . The anchoring portion may take any suitable form. In the embodiment shown throughout the Figures, the anchoring portion includes an anchoring stem  42  extending substantially longitudinally in the cannula passageway  20  from a location substantially at the intersection of the spokes  38 . A retaining prong  44  extends substantially longitudinally from the anchoring stem  42 , the retaining prong  44  having a radius larger than a radius of the retaining prong. Typically, although by no means exclusively, the retaining prong  44  has a substantially inverted conical configuration defining an annular retaining lip  46 . The retaining lip  46  and the adjacent surface of the spokes  38  define a disc-receiving spacing  48  therebetween. 
         [0066]    The diaphragm disc  34  is provided with a corresponding a mounting aperture  39  extending therethrough, the mounting aperture  39  having a radius substantially smaller than the radius of the retaining stem  42 , and more specifically of the retaining lip  46 . The resilient nature of the diaphragm disc  34  allows the diaphragm disc  34  to be stretched radially so as to allow the mounting aperture  39  to be fitted over the retaining prong  44  into the disc-receiving spacing  48 . This configuration of the valve allows to replace the diaphragm disc  34  should the diaphragm disc  34  become damaged, or should the needs of the intended user  14  change. For example, the diaphragm disc  34  could be exchanged for a diaphragm disc  34  having a different rigidity, or for a diaphragm disc  34  including a substance able to diffuse into the airflow passing thereby. 
         [0067]    The diaphragm disc  34  is located closer to the body proximal end  28  than the diaphragm frame  36 . Therefore, the resilient nature of the diaphragm disc  34  allows the latter to bend when subjected to a pressure imparted thereon. Typically, during the inspiration phase of breathing, the disc deforms substantially freely from a substantially flat closed configuration wherein it rests on the spokes  38  to an opened configuration shown in  FIG. 3  wherein it allows the flow of air through the cannula passageway  20 , particularly about the periphery thereof. 
         [0068]    In some embodiments of the invention, the diaphragm frame  36  and the diaphragm disc  34  have dimensions, configurations and deformation properties such that a substantially constant backpressure is exerted by the diaphragm disc  34  upon the intended user expiring air from the cannula proximal end towards  28  the cannula distal end  30  for a predetermined range of expiration flow rate. For example, the substantially constant backpressure is from about 0.1 cm H 2 O to about 100 cm H 2 O, and in some embodiments from about 0.5 cm H 2 O to about 20 cm H 2 O. In some embodiments of the invention, the predetermined range of expiration flow rate is from about 0.5 L/min to about 60 L/min, and in some embodiments, from about 10 L/min to about 40 L/min. 
         [0069]    Referring back to  FIG. 5 , there is shown that the proximal end of the ribs  38  adapted to contact the diaphragm disc  34  typically have a substantially pointed configuration defining an abutment apex  50 . The use of a relatively small contact surface between the spokes  38  and the diaphragm disc  34  is adapted to reduce adherence therebetween and, hence, to reduce resistance or inertia to the initial flow of air during the inspiration phase of breathing. 
         [0070]    The number of spokes  38 , their thickness, the spacing therebetween, and the thickness and material of the diaphragm disc  34  are typically calibrated so as to provide a predetermined resistance to the flow of air during the expiration phase of breathing. During the expiration phase of breathing, the diaphragm disc  34  is pushed back from its opened configuration shown in  FIG. 3  to the closed configuration wherein it abuts against the contacting apex  50  of the spokes  38 . 
         [0071]    Upon the pressure building up in the airway upstream from the nasal cannula  10  as a result of the air being blocked from flowing through the nasal passageway during the initial stage of the expiration phase of breathing, the internal pressure will eventually cause the diaphragm disc  34  to deform into a restricting configuration shown in  FIG. 2  wherein portions of the diaphragm disc  34  are deflected between the spokes  38  hence creating peripheral passageways  52  through which the air may be expelled out of the nose of the intended user. 
         [0072]    Hence, by using a substantially centrally anchored diaphragm disc  34  adapted to deform substantially about its periphery, a substantially constant resistance to air flow is provided during both the inspiration and expiration phases of breathing mainly because of the resilient nature of the diaphragm disc  34 . The resistance to air flow during the inspiratory phase will be less than the one during the expiratory phase of breathing. Furthermore, the delay of action of the valve is relatively short. Also, since the air will flow substantially peripherally, the air is distributed along the internal tissues of the nose hence improving the naturally occurring of heat exchange and humidification of the air flowing there through. Also, the diaphragm disc deflecting substantially peripherally and abutting against relatively small contact surfaces will have a tendency to be substantially silent and to have a relatively fast response time when the intended user switches between inspiration and expiration breathing. 
         [0073]    In some embodiments of the invention, as seen in  FIGS. 5 and 6 , the nasal cannula  10  is provided with a protective grid  54  or other suitable retaining means for ensuring that the diaphragm disc  34  remains within the cannula body  18  should the diaphragm disc  34  be unvoluntarily released from its anchoring means. The protective grid extends from the cannula body  18  and extends across the cannula passageway  20 . The protective grid  54  is located closer to the cannula proximal end  28  than the valve, and in some embodiments, is located substantially adjacent the cannula proximal end  28 . The protective grid  54  also increases the safety of the valved nasal cannula  10  by preventing relatively large objects from being inhaled by the intended user while the valved nasal cannula is inserted in the nostril  12 . 
         [0074]    In addition to, or independently from the valve, the nasal cannula  10  may be provided with a filtering medium and/or an air treating medium. For example, the nasal cannula  10  may be provided with an HEPA filter located within the cannula body  18  or any other suitable filter. The nasal cannula  10  may also be provided with a heat and/or humidity exchanger. The nasal cannula  10  may also be provided with a material mounted therein for dispensing a pharmaceutically active substance, an air treatment substance or any other suitable substance adapted to be activated by the breathing of the user and/or intrinsically active. 
         [0075]    As seen in  FIG. 7 , the nasal cannula  10 ′ is not necessarily frustro-conical and may present a substantially asymmetric configuration that better conforms to the shape of the nose of the intended user. 
         [0076]    As seen in  FIGS. 8 , a valved nasal cannula  10 ″ in accordance with an alternative embodiment of the invention includes a fixed spoke  38  extending substantially diametrically across the cannula passageway  20  and a mobile spoke  38 ″, the mobile spoke  38 ″ extending substantially diametrically across the cannula passageway  20  and being operatively coupled to the cannula body  18 ″ and to the fixed spoke  38  so as to be rotatable about the passageway longitudinal axis relatively thereto. In these embodiments, for example, the cannula body  18 ″ is substantially cylindrical. The mobile spoke  38 ″, by being angled at a variable angle relatively to the fixed spoke  38 , thereby influencing the deformation of the diaphragm disc  34  (not shown in  FIGS. 8 ) so as to adjust the backpressure produced by the cannula  10 ″. 
         [0077]    Mounting of the mobile spoke  38 ″ may be achieved by having a mounting shaft  56  extending substantially longitudinally from the center of the fixed spoke  38 . The mobile spoke  38 ″ is mounted to a substantially longitudinally extending sleeve  58  mounted onto the mounting shaft  56 . The mobile spoke  38 ″ defines notches  60  extending substantially radially inwardly thereinto. The cannula body  18 ″ defines substantially radially inwardly extending ledges  62  located so as to engage the notches  60 . The ledges  62  define recesses  68  for receiving the notches  60  at circumferentially spaced apart locations, thereby allowing to adjust in discrete steps the position of the mobile spoke  38 ″ relatively to the fixed spoke  38 . 
         [0078]    In some embodiments of the invention, as illustrated in  FIG. 9  the nasal cannula  10 ′″ is provided with a prehensile protrusion  80  of spoke  38 ′″ which provides a grabbing mean for easily removing the nasal cannula  10 ′″ out of the nostril vestibule. 
         [0079]    Although the present invention has been described hereinabove by way of preferred embodiments thereof, it can be modified, without departing from the spirit and nature of the subject invention as defined in the appended claims.