Patent Publication Number: US-11376378-B2

Title: Flow governors for use in medicinal inhalers

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a national stage filing under 35 U.S.C. 371 of PCT/US2016/067979, filed Dec. 21, 2016, which claims the benefit of U.S. Provisional Patent Application No. 62/270,064 filed Dec. 21, 2015 and U.S. Provisional Patent Application No. 62/289,651, filed Feb. 1, 2016, the disclosures of which are incorporated by reference in their entirety herein. 
    
    
     FIELD 
     The present disclosure generally relates to flow governors for use in medicinal inhalers, and flow governor assemblies and medicinal inhalers comprising the flow governors. 
     BACKGROUND 
     Delivery of aerosolized medicament to the respiratory tract for the treatment of respiratory and other diseases is conventionally done using inhalers of either the pressurised metered dose inhaler (pMDI), the dry powder inhaler (DPI) or the nebulizer type. pMDI inhalers in particular have become an industry standard, and are familiar to many patients who suffer from either asthma or from chronic obstructive pulmonary disease (COPD). Conventional pMDI devices comprise an aluminum canister, sealed with a metering valve, which contains the medicament formulation. Generally, the medicament formulation is a pressurized formulation containing either fine particles of one or more medicinal compounds suspended in a liquefied hydrofluoroalkane (HFA) propellant, or a solution of one or more medicinal compounds dissolved in a propellant/co-solvent system. Formulations incorporating one drug in solution and another one in suspension form are also known. 
     In a conventional pulmonary pMDI, the sealed canister is provided to the patient in an actuator. The actuator is conventionally a generally L-shaped plastic molding comprising a generally cylindrical vertical tube that surrounds the canister plus a generally horizontal tube that forms a patient port (e.g., a mouthpiece or nosepiece) that defines an inspiration orifice. To use such an inhaler, the patient exhales, places the patient port in a body cavity (e.g., mouth or nose) and then inhales to draw air through the inspiration orifice. (In the case of nasal pMDIs, it is not always necessary to inhale.) The majority of such inhalers are of the pulmonary “press-and-breathe” type, where the patient must press down on the protruding end of the canister in order to operate the metering valve to release a metered dose of medicament from the canister into the inhaled air stream and thence through the mouthpiece into their lungs. This requires a significant degree of coordination of timing of inhalation and dose release if the emerging cloud of aerosolized medicament is to be taken far enough into the lungs to provide maximum therapeutic benefit. If the patient releases the dose before inspiratory flow has been established, then a proportion of the drug is likely to be lost in the mouthpiece or the patient&#39;s mouth. Conversely, if released much after the start of inhalation, then the deeper regions of the lungs might already be full of air and not penetrated by the following bolus of released medicament aerosol. 
     To overcome what can be quite a challenge for some patients, pMDI device designs have been created that employ automatic breath-actuated triggering, releasing a dose only in response to the patient&#39;s inhaled breath. The AUTOHALER™ metered dose inhaler, available from 3M Company, St. Paul, Minn., and the EASIBREATHE™ inhaler, available from Teva Pharmaceutical Industries Ltd., Israel, are two such pMDI devices that use breath-actuation to attempt to better coordinate dose release with inhalation. 
     SUMMARY 
     Even though breath-actuated inhalers can be a useful aid in achieving coordination between inhalation and medicament dose release, with consequently improved medicament delivery to many patients&#39; lungs, these devices are however unable to overcome all the potential weaknesses that patients can exhibit in their inhaler use technique. For example, even if patients can achieve good timing of dose release, whether via breath-actuation or simply via good press-and-breathe coordination, they can have a tendency to inhale at sub-optimal flow rates. For example, very high inspiratory flow rates (i.e., volumetric flow rates) can give rise to excessive and problematic drug deposition on the back of the throat, while very low inspiratory flow rates can lead to poor entrainment of the aerosolized medicament spray. A related additional potential problem is that very high inspiratory flow rates can lead to more rapid filling of the lungs and consequently an even greater need for good coordination. 
     As a result of poor inhalation and dose release coordination, many patients do not get the full therapeutic benefit of their medicinal inhalers. For example, many patients with uncontrolled asthma are unable to (i) achieve a flow rate between 10 to 50 liters/minute (L/min.); (ii) maintain the flow rate for at least 1.5 seconds; and (iii) hold their breath for at least 5 seconds after inspiration. Poor inhaler use technique has been found to correlate to poor control of asthma. Similar considerations probably apply to other respiratory diseases treated using inhaled medication, e.g. to COPD. 
     The general view in the guidance provided by pharmaceutical companies is that pMDI medications should be taken with patients taking a slow and deep inhalation, normally interpreted as being less than 50-60 L/min. 
     For conventional pMDIs and other inhalers, however, the inhalation flow rate can be poorly controlled from one user to another and even from one breath to another for the same patient. Some patients can sometimes achieve flow rates as high as 250 L/min., while others can sometimes achieve an order of magnitude less Inhaling the medicament at a lower flow rate tends to reduce drug impaction in the upper airways and increases drug deposition deeper in the lung. If a patient is unable to control their asthma, or any other respiratory disease requiring use of an inhaler, this will impact their quality of life and may lead to the requirement for further medical intervention. 
     Spacer devices have previously been devised which fit onto the mouthpiece of a pMDI in order to reduce the velocity of the emergent plume of medicament aerosol and to provide a volume in which it can expand and its propellant can evaporate more completely. This serves to avoid some of the problems of coordination and also avoids the tendency for high throat deposition caused by excessively fast drug particle inhalation. However, spacer devices are very bulky, and they can retain an excessive proportion of the drug on their walls, thereby reducing the dose that reaches the patient. Spacer devices can also be highly sensitive to electrostatic charge, which can often be strongly affected by the way in which they are washed or dried. 
     Because the manner in which patients inhale through their pMDIs is an important determinant of the delivery of drug to their lungs and therefore of the benefits they obtain from their medication, the present inventors sought to control the inhalation profile. 
     A further difficulty arises in getting all patients to inhale in a similar and consistent manner. Inhaler designs each have their own inherent resistance (R) to air flow. This is often expressed in the units (Pa) 0.5 (min./L), and is related to inhalation air flow rate (FR) and patient-created pressure drop (PD) by the equation:
 
 R=PD   0.5   /FR.  
 
     Existing pMDI inhalers usually have low inherent resistances to air flow, for example below 0.5 Pa 0.5  min./L, which makes it difficult for patients to control their inhalation flowrate. 
     Breathing profiles can be too rapid. Breath-dosing coordination can be difficult under such circumstances, and both the inter-patient and intra-patient variability can be high. With resistances of this order it can also be difficult for patients to achieve a steady flow rate of a duration of more than perhaps 2 to 2.5 seconds. Flow rate consistency during an inspiratory maneuver, and between inhalations, can be difficult to obtain. For example, flow rate ‘spikes’ can occur, whereby patients achieve fairly high but very transient flow rates. This can lead to poor spatial distributions of drug in their airways. 
     However, adding a significant fixed (‘static’) resistance to the design of a pMDI device also poses problems. By restricting the geometry of the air flow path in an inhaler, much higher resistances could be created, for example 1.6 Pa 0.5  min./L or more. Such resistances are typical of some DPI devices, where a high resistance is required to generate the energy needed to disperse and/or de-agglomerate a dose of medicament powder from a system without the energy content of a liquefied propellant. Unfortunately, though, while high resistances make it much easier for many patients to inhale more slowly and steadily through an inhaler, and for a longer period (e.g. 5 seconds or more), they pose an obstacle to some weaker patients who struggle to inhale adequate amounts of air against such a resistance. COPD patients, in particular, often find it difficult to inhale through such high resistances because of their impaired lung function. 
     In order to overcome some of the above-described issues related to either a low or a high inhaler resistance, while also avoiding the need for a spacer device, the present inventors developed the flow governors of the present disclosure, which have the ability to change their geometry and resistance to air flow as a function of pressure drop experienced, i.e., between an inlet and outlet of the flow governor. Flow governors of the present disclosure (which can also be referred to as “flow rate limiters,” “flow limiters,” “flow regulators,” “flow limitation devices,” or derivations thereof) allow appreciable air flow rates at low differential pressures, while increasing air flow resistance at higher differential pressures in order to limit the air flow rates to values more consistent with those obtained at lower differential pressures to reduce inter-patient and intra-patient inhalation variability. 
     Some aspects of the present disclosure provide a flow governor for use in a medicinal inhaler. The flow governor can include (i) a tubular element that defines at least a portion of an air flow path, the tubular element comprising at least one flexible wall configured to flex inwardly in response to an air flow in the air flow path; and (ii) an internal support structure, located within the tubular element and configured to preserve at least a predetermined cross-sectional area of the air flow path within the tubular element when the at least one flexible wall of the tubular element flexes inwardly. 
     Other features and aspects of the present disclosure will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side cross-sectional view of a conventional pressurized metered dose inhaler (pMDI). 
         FIG. 2  is a graph schematically illustrating flow rate (L/min.) versus time (seconds) of inhalation flow profiles of COPD patients using conventional medicinal inhalers and using medicinal inhalers comprising a flow governor of the present disclosure. 
         FIG. 3  is an isometric view of a flow governor according to one embodiment of the present disclosure, shown at rest. 
         FIG. 4  is a front longitudinal cross-sectional view of the flow governor of  FIG. 3 , taken along line  4 - 4  of  FIG. 3 , shown at rest. 
         FIG. 5  is a transverse cross-sectional view of the flow governor of  FIGS. 3 and 4 , taken alone line  5 - 5  of  FIG. 3 , shown at rest. 
         FIG. 6  is a side longitudinal cross-sectional view of the flow governor of  FIGS. 3-5 , taken along line  6 - 6  of  FIG. 3 , shown at rest. 
         FIG. 7  is a transverse cross-sectional view of the flow governor of  FIGS. 3-6 , taken along line  5 - 5  of  FIG. 3 , shown in operation. 
         FIG. 8  is a side longitudinal cross-sectional view of the flow governor of  FIGS. 3-7 , taken along line  6 - 6  of  FIG. 3 , shown in operation. 
         FIG. 9  is a front longitudinal cross-sectional view of a flow governor according to another embodiment of the present disclosure, shown at rest. 
         FIG. 10  is a transverse cross-sectional view of the flow governor of  FIG. 9 , shown at rest. 
         FIG. 11  is a side longitudinal cross-sectional view of the flow governor of  FIGS. 9-10 , shown at rest. 
         FIG. 12  is a transverse cross-sectional view of the flow governor of  FIGS. 9-11 , shown in operation. 
         FIG. 13  is a side longitudinal cross-sectional view of the flow governor of  FIGS. 9-12 , shown in operation. 
         FIG. 14  is a front longitudinal cross-sectional view of a flow governor according to another embodiment of the present disclosure. 
         FIG. 15  is a side cross-sectional view of a medicinal inhaler according to one embodiment of the present disclosure, comprising the flow governor of  FIGS. 3-8  located in a dedicated air flow path and a cover over an open end of a housing that receives a medicament canister. 
         FIG. 16  is a side cross-sectional view of a medicinal inhaler according to another embodiment of the present disclosure, comprising the flow governor of  FIGS. 3-8  located in a dedicated air flow path and a skirt seal located between a medicament canister and a housing that receives the canister. 
         FIG. 17  is a side cross-sectional view of a medicinal inhaler according to another embodiment of the present disclosure, comprising the flow governor of  FIGS. 3-8  located in a cap configured to be coupled to an open end of a housing that receives a medicament canister. 
         FIG. 18  is a side cross-sectional view of a medicinal inhaler according to another embodiment of the present disclosure, comprising the flow governor of  FIGS. 3-8  located in a dedicated air flow path and one or more pressure sensors in fluid communication with the dedicated air flow path. 
         FIG. 19  is a side cross-sectional view of a breath-actuated medicinal inhaler according to one embodiment of the present disclosure, comprising the flow governor of  FIGS. 3-8  located in a dedicated air flow path. 
         FIG. 20  is a front longitudinal cross-sectional view of a flow governor assembly of a medicinal inhaler according to one embodiment of the present disclosure, comprising the flow governor of  FIGS. 3-8 , an upstream venturi, and one or more pressure sensors positioned in fluid communication with the flow governor. 
         FIG. 21  is an exploded isometric view of the flow governor assembly of  FIG. 20 . 
         FIG. 22  is a side longitudinal cross-sectional view of a portion of a flow governor assembly of a medicinal inhaler according to another embodiment of the present disclosure, comprising a flow governor according to one embodiment of the present disclosure, shown at rest. 
         FIG. 23  is a front longitudinal cross-sectional view of a portion of a flow governor assembly of a medicinal inhaler according to another embodiment of the present disclosure, comprising a flow governor according to one embodiment of the present disclosure, shown at rest. 
         FIG. 24  is a graph of inhalation pressure drop (kPa) versus inhalation flow rate (L/min.) for three different embodiments of flow governors of the present disclosure. 
         FIG. 25  is a graph of inhalation pressure drop (kPa) versus inhalation flow rate (L/min.) for three further embodiments of flow governors of the present disclosure. 
         FIG. 26  is a front longitudinal cross-sectional view of a flow governor according to another embodiment of the present disclosure, shown at rest. 
         FIG. 27  is a transverse cross-sectional view of the cross member of the flow governor of  FIG. 26 . 
         FIGS. 28A and 28B  are transverse cross-sectional views of alternative cross members of the flow governors of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure generally relates to a flow governor for use in a medicinal inhaler, the flow governor being adapted to change its geometry, and thereby its resistance to air flow, as a function of pressure drop between its inlet and its outlet. The flow governors of the present disclosure therefore provide a means of governing the air flow rate (i.e., volumetric flow rate) through a medicinal inhaler to reduce inter-patient and intra-patient inhalation variability and provide a more reproducible level of drug deposition in the lung. Such flow governors can provide a variable (dynamic) resistance to air flow in an air flow path of a flow governor assembly and/or medicinal inhaler. 
     Use of an inhaler incorporating one or more flow governors of the present disclosure could provide significant benefits to a sufferer of respiratory or other inhalation-treated disease. Apart from consistency of use and results, flow governors of the present disclosure can avoid the need for bulky spacer devices that are intended to reduce the need for such coordination. When used in conjunction with data recording of flow rates and other inhaler-use events and data, it can also improve physician monitoring of chronically ill patients. When two or more flow governors of the present disclosure are employed in a flow governor assembly and/or a medicinal inhaler, the flow governors can be arranged in parallel or in series. 
     Flow governors of the present disclosure can include (i) a tubular element that defines at least a portion of an air flow path therewithin, the tubular element comprising one or more flexible walls configured to flex (or collapse) inwardly in response to an air flow in the air flow path, and (ii) an internal support structure located within the tubular element and configured (e.g., shaped, dimensioned, positioned and having desired material properties) to preserve at least a predetermined cross-sectional area of the air flow path within the tubular element when the one or more flexible walls of the tubular element are flexed (or collapsed) inwardly. As a result, part of the air flow path cross-sectional area remains open even when the tubular element has collapsed, in order to allow the continued inhalation of air and emitted medicament. A “predetermined cross-sectional area of the air flow path within the tubular element” can include a portion of the air flow path that passes through the internal support structure, e.g., when the internal support structure includes one or more hollow portions or components, as well as a cross-sectional area of space between the tubular element and the internal support structure. The material makeup of the tubular element flexible walls can also be chosen to achieve the desired cross-sectional area between the tubular element and the internal support structure. 
     In some embodiments, calculation of the predetermined cross sectional area can be based on the flow resistance required to meet the governing requirements, for example, rearranging the following equation to find ‘A’:
 
 R =sqrt[0.5*ρ*( f*l/d+k )]/ A  
 
where:
 
     A=cross-sectional area (e.g., m 2 ) 
     ρ=air density (e.g., kg/m 3 ) 
     f=friction coefficient (dimensionless) 
     l=length of wall in in the flow direction (e.g., m) 
     d=tube diameter (e.g., m) 
     k=singular losses coefficient (dimensionless) 
     R=flow resistance (e.g., Pa 0.5 *min./L) 
     Ensuring that the predetermined cross sectional area is maintained can be achieved through use of the internal support structure which physically inhibits the tubular element from collapsing to a point where the cross sectional area is less than the predetermined cross sectional area, and may also include a suitable selection of the material makeup of the flexible walls of the tubular element. 
     At low inhalation flow rates, the patient experiences a low or moderate static resistance to air flow, but when the inhalation flow rate through the flow governor exceeds a certain flow rate, the tubular element partially collapses and thus imposes an additional resistance to air flow: the inhaler changes from being a low or medium resistance inhaler to a high resistance inhaler. That is, the flow governor provides variable resistance to the assembly comprising the flow governor and/or the inhaler comprising the flow governor (or flow governor assembly). 
     The present inventors discovered that it can be desirable to have a combination of a static medium resistance and a large variable resistance to make it easier for the patient to inhale with a specific (e.g., target) flow rate. There can be several contributors to the static resistance of a flow governor assembly (or inhaler), such as inlets, outlets, one or more constrictions, the flow governor, other geometrical features of the air flow path, or combinations thereof. As described in greater detail below with respect to  FIGS. 20-23 , such a constriction can include a venturi section, a narrow passageway, a tortuous path, or a combination thereof. The constriction can be used to add a desired amount of static resistance to the assembly (or inhaler), and can be separate and independent from the flow governor. For example, the constriction can be positioned (i) at a location in the housing upstream of the flow governor, and/or (ii) at a location in the housing downstream of the flow governor, such that the constriction is outside of and separate from the flow governor, i.e., to provide a known static resistance in addition to the flow governor. 
     The present inventors have recognized that a critical consideration is the balance of the static and variable resistances of a flow governor assembly (or inhaler) comprising a flow governor of the present disclosure, so that the flow governor assembly (or an inhaler comprising the flow governor assembly or the flow governor) can be used by a large proportion of weaker (e.g., COPD) patients with a minimum of inter-patient and intra-patient variability in inhalation flow rate. For example, as mentioned in the ‘Summary’ above, air flow resistance can be calculated according to the following equation:
 
 R=PD   0.5   /FR  
 
where:
 
     R=air flow resistance (e.g., Pa 0.5 *(min./L) 
     PD=pressure drop (e.g., Pa) 
     FR=volumetric air flow rate (e.g., L/min.) 
     Particularly, the present inventors discovered that at low pressure drops (e.g., 0.5 kPa), a flow governor assembly (or inhaler) having a properly balanced static and dynamic air flow resistance can exhibit a first overall air flow resistance R 1 , based on the static resistance of the assembly (or inhaler) comprising the flow governor. At higher pressure drops (e.g., 4 kPa), the flow governor assembly (or inhaler) can exhibit a second air flow resistance R 2 , predominantly based on the relatively large dynamic resistance provided by the flow governor. As a result, the balance of static and dynamic resistances can exhibit appropriate overall air flow resistances at both low pressure drops and high pressure drops to achieve a target governing flow rate over a range of pressure drops. 
     In some embodiments, the ratio of R 2 /R 1  (e.g., at a given volumetric flow rate, or to achieve a target governing volumetric flow rate) of a flow governor assembly (or inhaler) comprising the flow governor (and optionally, further comprising a constriction to introduce a desired level of static resistance) can be at least 1.2; in some embodiments, at least 1.3; in some embodiments, at least 1.5; and in some embodiments, at least 2. In some embodiments, the ratio of R 2 /R 1  (e.g., at a given volumetric flow rate, or to achieve a target governing volumetric flow rate) can be no greater than 3; in some embodiments, no greater than 2.9; in some embodiments, no greater than 2.8; in some embodiments, no greater than 2.7; in some embodiments, no greater than 2.5; and in some embodiments, no greater than 2. 
     In some embodiments, a flow governor assembly (or inhaler) comprising the flow governor can provide an overall resistance (e.g., R 1 ) to air flow of at least 0.4 Pa 0.5 *min./L at a pressure drop (i.e., between an air inlet and an air outlet of the air flow path of the assembly (or inhaler)) of 0.5 kPa. In some embodiments, the overall resistance to air flow can be at least 0.5 Pa 0.5 *min./L at 0.5 kPa; and in some embodiments, at least 0.6 Pa 0.5 *min./L at 0.5 kPa. In some embodiments, the overall resistance can be no greater than 1.2 Pa 0.5 *min./L at 0.5 kPa; in some embodiments, no greater than 1.1 Pa 0.5 *min./L at 0.5 kPa; in some embodiments, no greater than 1.0 Pa 0.5 *min./L at 0.5 kPa; in some embodiments, no greater than 0.8 Pa 0.5 *min./L at 0.5 kPa; and in some embodiments, no greater than 0.7 Pa 0.5 *min./L at 0.5 kPa. 
     In some embodiments, the overall resistance (e.g., R 2 ) can be at least 1 Pa 0.5 *min./L at 4 kPa; in some embodiments, at least 1.1 Pa 0.5 *min./L at 4 kPa; in some embodiments, at least 1.2 Pa 0.5 *min./L at 4 kPa; and in some embodiments, at least 1.5 Pa 0.5 *min./L at 4 kPa. In some embodiments, the overall resistance can be no greater than 3.2 Pa 0.5 *min./L at 4 kPa; in some embodiments, no greater than 3 Pa 0.5 *min./L at 4 kPa; in some embodiments, no greater than 2.5 Pa 0.5 *min./L at 4 kPa; in some embodiments, no greater than 2.2 Pa 0.5 *min./L at 4 kPa; in some embodiments, no greater than 2.0 Pa 0.5 *min./L at 4 kPa; and in some embodiments, no greater than 1.8 Pa 0.5 *min./L at 4 kPa. 
     In some embodiments, the overall resistance to air flow at low pressure drops (e.g., 0.5 kPa), R 1 , can range from about 1.1 to about 0.4 Pa 0.5 *min./L (e.g., to achieve a governing flow rate ranging from about 20 L/min. to about 60 L/min.); and in some embodiments, can range from about 0.8 to about 0.6 Pa 0.5 *min./L; and in some embodiments, can range from about 0.7 to about 0.5 Pa 0.5 *min./L. 
     In some embodiments, the overall resistance to air flow at high pressure drops (e.g., 4 kPa), R 2 , can range from about 3.2 to about 1.0 Pa 0.5 *min./L (e.g., to achieve a governing flow rate ranging from about 20 L/min. to about 60 L/min.); and in some embodiments, can range from about 2.5 to about 1.5 Pa 0.5 *min./L; and in some embodiments, can range from about 2.3 to about 1.8 Pa 0.5 *min./L. 
     The flow governors of the present disclosure are suitable for use in multiple forms of inhalers for the delivery of doses of medicament in the form of aerosols to the respiratory tract, including oral pulmonary inhalers and nasal inhalers. Flow governors of the present disclosure are suitable for use in a variety of inhalers, including but not limited to, one or more of a pressurized metered dose inhaler (pMDI) (e.g., a press-and-breathe pMDI, a mechanical (i.e., mechanically triggered) breath-actuated pMDI, an electronic (i.e., an electronically triggered) breath-actuated pMDI, or a combination thereof); a dry powder inhaler (e.g., a single dose (e.g., capsule) DPI, a multi-dose (e.g., tape based, or reservoir based) DPI, or a combination thereof); a nebulizer (e.g., a pocket nebulizer); or a combination thereof. 
     GB Patent No. 2266466 discloses an exemplary electronically triggered breath-actuated pMDI that could be modified to incorporate a flow governor of the present disclosure. PCT Publication No. WO 2015/34709 discloses an exemplary DPI that could be modified to incorporate a flow governor of the present disclosure. PCT Publication No. WO 92/12799 discloses an exemplary pocket nebulizer that could be modified to incorporate a flow governor of the present disclosure. A flow governor of the present disclosure can be used in any of the inhalers disclosed in GB Patent No. 2266466, PCT Publication No. WO 2015/34709, PCT Publication No. WO 92/12799 (each of which is incorporated herein by reference in its entirety), or a combination thereof. 
     For example, some embodiments of the present disclosure provide a medicinal inhaler comprising a flow governor and a breath actuation mechanism. In some embodiments, the breath actuation mechanism can be configured to trigger to release a dose of medicament at an inspiratory flow rate less than a governing flow rate of the flow governor. 
     Generally, it is important that the triggering flow rate is not set too low, to avoid the risk that the breath-actuated inhaler might operate accidentally or that it will deliver the medicament at too low an inhalation rate for adequate therapeutic effect. It is also important that the triggering flow rate is not set so high that a patient (e.g. a weak COPD patient) cannot achieve the triggering flow rate. 
     The triggering flow rate of the breath-actuation system needs to be below the governing air flow rate, in order that the latter does not prevent the triggering flow rate from being achieved. For example, in some embodiments, the target triggering flow rate of an inhaler can be 15 liters/minute (L/min.) and the target governing flow rate can be 30 L/min. In reality, a “target governing flow rate” may actually include a range of flow rates, as described in the Examples section with reference to  FIGS. 24 and 25 , such that the target governing flow rate may actually be a target range of flow rates. Manufacturing tolerances can be maintained such that individual inhalers all have an actual triggering flow rate of significantly less than their governing flow rate. Environmental factors such as temperature and atmospheric pressure will also broaden the range of values actually obtained. For example, actual triggering flow rates might vary between 10 L/min. and 20 L/min., and actual governing flow rates might vary between 25 L/min. and 35 L/min. 
     Some embodiments of the present disclosure provide a medicinal inhaler comprising a flow governor and an inspiratory air flow detection (or “inspiratory flow rate detection system,” or “air flow detection system,” or “flow rate detection system,” or derivations thereof) and/or measurement system. In some embodiments, such a detection system can include at least one pressure sensor located in the inhaler and configured to allow the inspiratory air flow rate to be sensed. For example, at least one pressure sensor can be located upstream of the flow governor in an air flow path of the medicinal inhaler. In some embodiments, such a detection system can include (i) a pressure sensor located in fluid communication with the air flow path, upstream of the flow governor, and (ii) a venturi constriction in the air flow path located adjacent where the pressure sensor is in fluid communication with the air flow path. Such a venturi constriction can speed up the local air velocity to enhance the sensitivity of the pressure sensor, allowing for less sensitive, and less costly, sensors to be employed. Such a detection system can further include a second pressure sensor located in fluid communication with the air flow path, downstream of the flow governor, such that air flow direction can be determined, i.e., in order to distinguish between inhalation and exhalation. 
     Some embodiments of the present disclosure provide a medicinal inhaler comprising a flow governor, a breath actuation mechanism, and an inspiratory air flow detection system. 
     In some embodiments of the present disclosure, the breath-actuation system can be an electronically triggered breath-actuation system. For example, the one or more pressure sensors can provide an electrical signal which is used to trigger dose release according to a defined algorithm. The dose release system may be a mechanical system, triggered by the electronic system&#39;s algorithm. Optionally, the electronic system may be housed in a reusable module, in order to reduce the overall cost of a prolonged period of treatment. 
     Additional details of flow governors and inspiratory air flow detection systems in combination with flow governors are described in PCT Publication No. WO2017/112452, which is incorporated herein by reference in its entirety. 
     Dose release firing systems that can be employed in combination with flow governors of the present disclosure are described in PCT Publication No. WO2017/112476 and PCT Publication No. WO2017/112400, each of which is incorporated herein by reference in its entirety. In addition, auto-reset dose release firing systems that can be employed in combination with flow governors of the present disclosure are described in PCT Publication No. WO2017/112451, which is incorporated herein by reference in its entirety. 
     Some firing systems (e.g., which can be used in combination with flow governors of the present disclosure) can produce a small time delay between the start of inhalation and the time when the medication is released. Desirably, medication release occurs within 0.5 sec of the start of inhalation. A typical COPD patient has a tidal lung capacity of about 1.5 L. If the inhalation flow rate is limited by the flow governor to about 30 L/min., then the time of inhalation could be expected to extend to about 3-4 seconds. In reality, COPD patients may not be able to inhale for this long, due to their poor lung function, but it is anticipated that there will be sufficient time for drug to be transferred to the lung. 
     Some embodiments of the present disclosure provide a method of treatment of a pulmonary condition in a human patient, the method comprising: (i) providing a medicinal inhaler incorporating a flow governor comprising the tubular element and internal support structure described above; (ii) inserting a patient port of the medicinal inhaler into a body cavity (e.g., a mouth or nose); and (iii) actuating the medicinal inhaler while inhaling. 
     In some embodiments, the present disclosure can provide a method of using a medicinal inhaler, or of treating a pulmonary condition, which can include providing a flow governor of the present disclosure in an air flow path of the medicinal inhaler, and varying an air flow resistance of the inhaler in response to air flow in the air flow path of the flow governor. The method can further include inserting a patient port into a body cavity; and inhaling through the patient port to cause air flow in the air flow path of the flow governor. Varying the air flow resistance of the inhaler can include flexing one or more tubular walls of a tubular element of the flow governor inwardly toward an internal support structure located within the tubular element, the internal support structure configured to preserve at least a predetermined cross-sectional area of the air flow path within the tubular element when the one or more tubular walls flexes inwardly. 
     Definitions 
     The terms “a”, “an”, and “the” are used interchangeably with “at least one” to mean one or more of the elements being described. 
     The term “and/or” means either or both. For example “A and/or B” means only A, only B, or both A and B. 
     The terms “including,” “comprising,” or “having,” and variations thereof, are meant to encompass the items listed thereafter and equivalents thereof as well as additional items. 
     Unless specified or limited otherwise, the terms “connected” and “coupled” and variations thereof are used broadly and encompass both direct and indirect connections and couplings. 
     Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. 
     The term “flexible” is used to refer to a material and/or structure that collapses or significantly deforms in response to an air pressure differential existing across the material and/or structure in its typical mode of operation. The term ‘rigid’ is used to refer to a material and/or structure that does not collapse or significantly deform under the forces it experiences in its typical mode of operation. For example, the tubular element of flow governors of the present disclosure is generally flexible and deformable in its normal operation, whereas the internal support structure of flow governors of the present disclosure is generally rigid or non-deformable in its normal operation. 
     The term “tubular” is used to refer to a hollow structure having one or more walls that define an open passageway therein. In some embodiments, the term “tubular” can more specifically refer to elongated hollow structures. Tubular elements of flow governors of the present disclosure or tubular air flow paths of the present disclosure can have any cross-sectional shape desired (i.e., transverse cross-sectional shape—taken substantially orthogonally with respect to a longitudinal axis of the tubular structure), including, but not limited to, one or more of circular, elliptical or oblong (i.e., having a longer major axis and a shorter minor axis), triangular, rectangular, square, trapezoidal, polygonal, star-shaped, D-shaped, other suitable cross-sectional shapes, or a combination thereof. In some embodiments, tubular structures of the present disclosure can have a circular cross-sectional shape. 
     The present disclosure will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may for illustrative purposes be exaggerated and not drawn to scale. Identical, similar or equivalent features in different embodiments have been denoted by similar numerals but with the addition to them of 100, 200, 300, etc. 
     Before describing the embodiments in accordance with the present invention, a typical embodiment of a conventional pMDI device will be described with reference to  FIG. 1 . 
       FIG. 1  illustrates a conventional pressurized metered dose inhaler (pMDI)  50  comprising a canister  51  containing a medicament formulation  52 , the canister comprising a can  53  sealed with a metering valve  54 . The canister  51  sits within a housing (or “actuator”)  55  comprising a tubular sleeve portion  56  having an open end  47  dimensioned to receive the canister  51  and from which its base  49  can protrude, and a portion in the form of a patient port  57  (e.g., in the form of a mouthpiece) that defines an inspiration orifice (or an air outlet)  45 . Such a patient port of an inhaler is sometimes referred to herein as a “mouthpiece” for simplicity. However, it should be understood that such mouthpieces can instead be configured to be nosepieces of nasal inhalers and that the present disclosure can equally apply to nasal inhalers even where not specifically mentioned herein. The open end  47  of the housing  55  can define an aspiration orifice, or an air inlet, and the air outlet  45  can define an inhalation orifice, or an air outlet. 
     A stem portion  58  protrudes from the metering valve  54  and is located and retained by friction in a stem socket  59  formed as an integral part of the housing  55 . A spray orifice  60  is formed in the stem socket  59 , and provides a passage for fluid communication between the valve stem portion  58  and the inspiration orifice  45 . In use, a patient places the patient port (e.g., mouthpiece)  57  into a body cavity (e.g., mouth) and then inhales through it while at the same time pressing downwards on the protruding base  49  of the canister  51 . The pressing force serves to move the canister  51  downwards relative to the valve&#39;s stem portion  58 . That relative movement serves to isolate a metered dose of medicament formulation from the bulk formulation in the canister  51  and then to discharge it via a hollow bore  48  formed in the stem portion  58 . The discharged dose then passes along the fluid passageway through the stem socket  59  and the spray orifice  60  and emerges in the form of a fine respirable spray  61  that passes through the patient port  57  into the patient&#39;s body cavity (e.g., oral cavity and/or nasal cavity) and thence into their respiratory passages, thereby treating their disease. 
     Important aspects of such a conventional pMDI device  50  that have the potential to limit its efficacy are, in particular, its fixed low resistance to air flow and its need for good patient coordination between the timing of the start of inhalation and the moment at which the canister  51  is pressed downwards. The latter is a challenge for a high proportion of patients, leading to poor and often highly varying efficacy of medicament administration. 
     The low resistance air flow path is best described with reference to  FIG. 1 . As the patient inhales on the patient port  57 , i.e. as they reduce the air pressure in their own respiratory passages and oral cavity and in the patient port  57  via outward movement of their chest wall and downwards movement of their diaphragm, an air flow is set up through the pMDI device  50 . Air from the atmosphere external to the inhaler, i.e., ambience, is drawn into the inhaler via an air flow path  46  of the pMDI device  50 , e.g., beginning with the annular gap between the can  53  and the open tubular sleeve portion  56  of the housing  55 , passing down the sleeve portion  56  along the length of the can  53 , and turning the corner into the wide passageway inside the mouthpiece  57 . The mouthpiece passageway clearly needs to be open and wide to allow the medicament spray  61  to emerge. The annular gap also has a large cross-sectional area that is approximately a product of the canister diameter (typically 22-23 mm) and the clearance required between the canister  51  and the housing sleeve portion  56  to ensure that the canister  51  does not scrape or jam within the housing  55 . Typically this clearance is 2 mm or more, giving an approximate air flow path cross-sectional area of in excess of 40 mm 2 . At the typical patient inspiratory pressure drops of 0.5 to 8 kPa, that cross-section presents very little effective resistance to inspiratory air flow. It is thus easy for many patients to draw an excessive and uncontrolled flow rate of air through the inhaler, leading to poorly controlled and inconsistent medicament delivery to their lungs. 
       FIG. 2  shows, schematically, some fairly typical chronic obstructive pulmonary disease (COPD) patient inspiratory flow rate (L/min.) versus time (seconds) profiles. In the absence of significant inhalation device resistance to air flow, some profiles  29  are characterised by a short, relatively rapid intake of breath. Other patients, e.g. with weaker lungs, are unable to either sustain long inhalations or to achieve adequate flow rates. Their profiles  31  are short and weak. Using an inhaler that comprises a flow governor of the present disclosure, however, can provide patient inspiratory profiles that are more like that denoted as  33 : a longer, sustained, steady inspiratory flow rate (e.g., of around 30 L/min.) can be obtained. 
     COPD patients have a wide range of inhalation breathing capability and this can be represented as a distribution between 0.5 and 4 kPa pressure drop. In some embodiments, the static resistance of an inhaler of the present disclosure prior to any governing of flow by the flow governor of the present disclosure (i.e., prior to any collapse of the tubular element) can be approximately 0.8 Pa 0.5  min./L. This can be considered to be a medium resistance. In some embodiments of the present disclosure, the target governing flow rate can be 30 L/min. In some embodiments, the target breath-actuation triggering flow rate can be 15 L/min. With such a system, there is very low probability of a COPD patient not being able to reach the triggering flow rate, either through lack of inhalation effort or because any individual flow governor limits the air flow rate to less than its breath-actuation triggering flow rate. Such an inhalation device is therefore suitable for a very high proportion of COPD patients. That is, at low flow rates, the inhaler will operate like a medium resistance device, and every patient will be able to inhale up to 20 L/min. quite easily. At a somewhat greater flow rate, the flow governor&#39;s tubular element will collapse onto the internal support structure, and the inhaler will become a high resistance device. The patient will then not be able to inhale at a higher flow rate. In general, patients are likely to learn to automatically compensate their inhalation effort and will continue to inhale at a flow rate that is comfortable to them. For some patients, that will involve a pressure drop of only 0.5 kPa, but for others it will be 4 kPa or above depending upon their lung strength and capacity and upon the training the patient has previously had. 
     If a higher flow governor flow rate were selected (e.g., greater than 30 L/min.), then some patients would not be able to achieve the air flow rate required for the inhaler to be governed, and the variability in patient inhalation would not be minimized. If, alternatively, the inhaler were to have a higher resistance, then again some patients would not be able to achieve the governed flowrate and the variability in patient inhalation flowrate would not be minimized. With the parameters described above, however, an inhaler incorporating a flow governor of the present disclosure has the potential to:
         Improve coordination of drug release with the start of inspiratory flow;   Maintain the inspiratory air flow rate to within a range of approximately 25 to 35 L/min.; and   Reduce variability both in dose consistency and the location of drug deposition in the lung.       

     For a nominal target governing flow rate of 30 L/min., there will be a range of actual values due to manufacturing tolerances and environmental factors such as temperature and atmospheric pressure. In an embodiment where the inhaler&#39;s total static resistance is 0.83 Pa 0.5 (minl −1 ), and the flow governor has a nominal governing flow of 30 L/min., any patient inhaling at a pressure drop between 0.5 kPa and 4 kPa would be expected to generate an air flow of between about 25 and 35 L/min. 
     In some embodiments of the present disclosure, the governing flow rate can be nominally 40 L/min. In this case, patients who can only produce a low inhalation pressure drop (e.g. about 0.5 kPa) and who typically inhale at less than 40 L/min. will not benefit from the flow governor, and their inhalation will be equivalent to inhaling through a medium resistance inhaler. Other patients who naturally inhale more strongly (i.e. at a higher pressure drop) are likely to benefit from the flow governor, and their flow rate will be restricted by the flow governor to the governing flow rate. 
     In some embodiments of the present disclosure, the governing flow rate can be nominally 50 L/min. In this case, only patients who inhale at a pressure drop of greater than approximately 1.5 kPa will experience flow governing. Because the governing flow rate is higher, there will be a larger spread in the Peak Inhalation Flow rates (PIF) obtained between patients: some will be able to inhale at only around 27 L/min. because this is the fastest that they can inhale through a medium resistance device, whereas others who inhale at 4 kPa could pull as much as 55 L/min. through the system. 
     Additional illustrations of the effects of flow governors are detailed below in the Examples section. 
       FIGS. 3-14  illustrate various embodiments of flow governors of the present disclosure.  FIGS. 15-19  illustrate various embodiments of medicinal inhalers of the present disclosure that comprise a flow governor of the present disclosure.  FIGS. 20-23  illustrate various embodiments of flow governor assemblies of the present disclosure, comprising flow governors that can be employed in medicinal inhalers. 
     Flow Governors 
       FIGS. 3-8  illustrate a flow governor  101  according to one embodiment of the present disclosure.  FIGS. 3-6  show the flow governor  101  at rest, and  FIGS. 7-8  show the flow governor  101  in operation. 
     As shown, the flow governor  101  includes an outer flexible tubular element (or “tube”)  102  comprising at least one flexible wall  140 , and an internal support structure  103  that is dimensioned to be received within the tubular element  102  (i.e., within the at least one flexible wall  140 ). In the embodiment of  FIGS. 3-8 , the internal support structure  103  includes a hollow base  104 , two hollow (e.g., tubular) pillars  105  and a cross member (or “crossbeam”)  106 . 
     The outer diameter of the hollow base  104  of the illustrated embodiment is greater than an initial inner diameter of the tubular element  102 , and assembly of the two components can be achieved by stretching the tubular element  102  over an outer portion (e.g., an outer wall) of the hollow base  104 . This positioning results in the originally circular cross-section of the tubular element  102  being deformed into an approximately elliptical (or oblong) cross-sectional (i.e., in transverse cross-section) shape. In some embodiments, such an elliptically-shaped tubular element  102  can have a major axis (externally) of approximately 12 mm and a minor axis (externally) of approximately 4 mm. 
     Other formation and/or assembly means are alternatively possible, however, as will be apparent to a person of ordinary skill in the art. For example, the tubular element  102  could instead be over-molded onto an outer surface of the hollow base  104  of the internal support structure  103 , or it could be stretched and then coupled to the outer surface of the base  104  by a variety of coupling means, including, but not limited to, one or more of adhesives, cohesives, welding (e.g., sonic [e.g., ultrasonic] welding), any thermal bonding or heat sealing technique (e.g., heat and/or pressure applied to one or both of the components to be coupled), other suitable coupling means, or combinations thereof. 
     In some embodiments, the internal support structure  103  can be coupled to or integrally formed with a portion of a housing that forms an air flow path or an inhaler of the present disclosure. For example, in some embodiments, the internal support structure  103  can be provided by (e.g., integrally formed with) the housing that forms at least a portion of an inhaler housing. 
     As shown in  FIGS. 3-6 , the flow governor  101 , and the tubular element  102 , can be substantially linear. Furthermore, the flow governor  101  can have an air flow path  107  including an air inlet  108  located at a first (longitudinal) end and an air outlet  109  located at a second (longitudinal) end that generally define an air flow direction that is generally oriented along a longitudinal direction D. The tubular element  102  can be elongated in the longitudinal direction D. The at least one flexible wall  140  of the tubular element  102  can be oriented substantially parallel to the longitudinal direction D; the hollow pillars  105  can be oriented substantially parallel to the longitudinal direction D; and the cross member  106  can be oriented at a non-zero angle (e.g., substantially perpendicularly) with respect to the longitudinal direction D, i.e., substantially parallel with respect to a lateral direction L (which can represent a side-to-side direction of the flow governor  101 ). A third transverse direction T is oriented substantially perpendicularly with respect to the longitudinal direction D and the lateral direction L, and can represent a front-to-back direction of the flow governor  101 . 
     The tubular element  102  (i.e., the at least one flexible wall  140 ) can be formed of a variety of materials, including, but not limited to, one or more of silicone rubber, other thermoplastic elastomers, or combinations thereof. In addition to its flexibility, the tubular element  102  can be formed of a material that is resilient, in order that it returns to its rest shape and position when air flow through it ceases, i.e., the tubular element  102  can deform elastically and spring back ready for its next cycle of use. The material may be chosen according to specific property needs, e.g. if it is to be over-molded, glued or ultrasonically welded to the hollow base  104  of the internal support structure  103 . It will be obvious to one skilled in the art that the chosen tubular element material should have good long term physical and chemical stability. 
     While the tubular element  102  can suitably have a relaxed transverse cross-sectional shape that is substantially circular (and which can be stretched to an elliptical cross-sectional shape over the base  104  of the internal support structure  103 ), other cross-sectional shapes are possible, such as those described above in the definition of “tubular.” It should also be noted that the base  104  can be elliptical in its transverse cross-sectional shape or can be another shape. In some embodiments, the base  104  is elliptical, the ellipse having the special case shape of a circle. In some embodiments employing a transverse cross-sectional shape of the base  104  that is circular, or is close to circular, can assist in ensuring that the tubular element  102  can be assembled onto it without imposing significant residual torsional strains into it. Furthermore, in some embodiments, the tubular element  102  can be formed of more than one material, or can have different sections (e.g., sequentially along its longitudinal direction) with different wall thicknesses and/or diameters, such that certain sections of the tubular element  102  are more flexible than others and can preferentially collapse. 
     In some embodiments, the tubular element  102  can be formed of a silicone rubber tube of approximately 0.3 mm wall thickness, 8.0 mm initial inside diameter, 20 mm length and 60 OO Shore hardness. 
     In some embodiments, the internal support structure  103  can have an “H” shaped longitudinal cross-sectional shape (i.e., taken along the longitudinal direction D), as shown in  FIG. 4 . However, as shown in  FIG. 4 , in some embodiments, the cross member  106  may not be longitudinally centered with respect to the overall dimension (e.g., height) of the internal support structure  103  in the longitudinal direction D, but rather, the cross member  106  may be located toward the air inlet end (e.g., an upstream end) of the internal support structure  103 . 
     Additionally, or alternatively, in some embodiments, the internal support structure  103  can have a generally “H” shaped (i.e., generally similar to a capital English letter H) transverse cross-sectional shape (i.e., taken substantially orthogonally with respect to the longitudinal direction D, e.g., in the lateral direction L or the transverse direction T), as shown in  FIG. 5 . Furthermore, in some embodiments, the internal support structure  103  can be formed of an injection molded plastic, such as polypropylene, acetal, ABS (acrylonitrile butadiene styrene), polycarbonate or polyethylene, or can be made from a metal or metal alloy (e.g., machined, stamped/pressed or metal injection molded) or from a ceramic material (e.g. ceramic injection molded). In some embodiments, the internal support structure  103  can be formed as a single integral component, i.e., formed from one part. 
     As shown in  FIG. 5 , in some embodiments, the cross member  106  of the internal support structure  103  can be substantially centered with respect to the pillars  105  in the transverse direction T, which gives the generally “H” shaped transverse cross-sectional shape. In addition, by way of example, the illustrated internal support structure  103  of  FIGS. 3-8  has lateral symmetry about a central longitudinal axis (i.e., about a central transverse-longitudinal plane), as well as transverse symmetry (e.g., front-to-back) about the central longitudinal axis (i.e., about a central lateral-longitudinal plane). Said another way, the internal support structure  103  is symmetrical about a central longitudinal axis in the lateral direction D and the transverse direction T. 
     As will be described in greater detail below, only the air outlet end of the tubular element  102  is fixed and supported (i.e., by the base  104  of the internal support structure  103 ), whereas the air inlet end of the tubular element  102  is freestanding and able to collapse onto the internal support structure  103 . 
     The assembly of the tubular element  102  and the internal support structure  103  forms the air flow path  107 , including the air inlet  108  and the air outlet  109 .  FIG. 5  shows a transverse cross-section of the flow governor  101 , which illustrates that the tubular element  102  has an approximately elliptical cross-section once stretched onto the base  104  of the internal support structure  103 , and also shows two lumens  110 , located within the two hollow pillars  105 , which act as residual air flow channels, i.e., function as a portion of the air flow path  107  through the flow governor  101 . By way of example only, the lumens  110  are shown as having an approximately triangular shape in the transverse cross-section. In some embodiments, each of the two lumens  110  can have an open cross-sectional area of approximately 1 mm 2 . 
       FIG. 6  shows a side longitudinal cross-section of the flow governor  101 , which illustrates that the tubular element  102  runs substantially parallel to the hollow pillars  105 , but is not in contact with them. At the air inlet  108 , the hollow pillars  105  can protrude from the tubular element  102 . With reference to  FIG. 4 , it may be noted that air flow entering the pillar lumens  110  will exit at a bypass outlet  111  of each pillar  105 , prior to passing through the hollow base  104 . 
     One primary function of the flow governors of the present disclosure is to govern air flow when the patient inhales through a medicinal inhaler, limiting the patient&#39;s inspiratory flow rate to a narrow and controlled range in order to avoid excessively fast inhalation and consequently excessive mouth and throat drug deposition. The flow governors of present disclosure are thus able to aid in the attainment of increased deep lung drug penetration and deposition. 
     Use of such a flow governor allows patients with poor lung function (e.g. particularly poorly COPD patients) to experience a relatively low inhaler air flow resistance (allowing them to inhale sufficient air in a reasonable degree of comfort) while giving patients with stronger lungs a transiently higher air flow resistance to inhale against (thereby allowing them to inhale for longer and more deeply, while at the same time limiting their inhalation air flow rate to a level very similar to that of weaker patients). In other words, the inspiratory air flow rate can be kept much more consistent between patients and between inhalations. Medication delivery is thus much more predictable, allowing physicians to prescribe treatment regimes with an improved level of confidence. 
     While  FIGS. 3-6  illustrate the flow governor  101  at rest (i.e., with the tubular element  102  in an uncollapsed state);  FIGS. 7 and 8  show the flow governor  101  in an operative state (i.e. with the patient&#39;s inspiratory air flow substantially passing through it and with the tubular element  102  in a collapsed state). When air is sucked towards the air outlet  109 , it flows via the air inlet  108  into the air flow path  107 , around the pillars  105  and cross member  106  (i.e., through any gap still present between the pillars  105  and the tubular element  102  and between the cross member  106  and the tubular element  102 ), and through the pillar lumens  110 . The speed of the passing air flow through the air flow path  107  creates a reduction in air pressure in the air flow path  107  (i.e., according to the Bernoulli Effect). In the embodiment illustrated in  FIGS. 3-8 , the reduced pressure in the air flow path  107  causes a reduction in the diameter along the minor axis of the elliptical cross-sectioned tubular element  102  (i.e., in the transverse direction T) resulting in inward bending, as shown in  FIGS. 7 and 8 . Because the tubular element  102  is supported at one end (i.e., its outlet end, toward the air outlet  109 ) by the hollow base  104 , the inward bending occurs predominantly at the end of the tubular element  102  that is towards the air inlet  108 , the inward bending restricting the cross-sectional area of the air flow path  107 . 
     To an extent, the greater the reduction in pressure in the air flow path  107 , the greater the inward bending of the tubular element  102 . The resultant reduction in the cross-sectional area of the air flow path  107  leads to an increased resistance to air flow rate. However, because the air flow path  107  of the flow governor  101  is only one part of the total overall resistance to air flow of the medicinal inhaler in which the flow governor  101  is employed (e.g. it might be around 50% or less of the total inhaler air flow resistance if the inhaler has a moderate static resistance to air flow), then the mass flow rate of air through the flow governor  101  does not fall in proportion to its reduced residual cross-sectional area. This means that the velocity of air through the residual air flow path  107  within the collapsed tubular element  102  rises as the tubular element  102  collapses, further increasing the Bernoulli forces upon it. This effect tends to lead to substantial bistability in the operation of the flow governor  101 . That is, the initiation of collapse leads to “positive feedback” which reinforces the inwards collapse-driving Bernoulli forces until they are eventually balanced by the resistive stiffness forces of the material of the tubular element  102 . In other words, in some embodiments, the flow governor  101  can be substantially bistable, where it tends to be in one of two states at any time: either it is in a substantially ‘open’ or ‘uncollapsed’ state, or it is in a substantially ‘collapsed’ state. 
     Complete collapse of the elliptical cross-section tubular element  102  is prevented by the hollow pillars  105 . These pillars  105 , together with the cross member  106 , provide structural support that prevents significant reduction in the diameter along the major axis of the elliptical cross-section tubular element  102  (i.e., in the lateral direction L). The air flow bypasses provided by the lumens  110  allow a base level of residual air flow to continue to flow. In addition, the finite stiffness of the tubular element  102  means that small additional gaps are left around the corners of the internal support structure  103  where the tubular element  102  cannot bend sufficiently to close off all the small residual air passageways or gaps between the internal support structure  103  and the tubular element  102  (see, e.g.,  FIG. 7 ). Thus, at least a minimum, or residual, air flow can always continue to flow. That is, the reduced pressure can never reach a value sufficient for the tubular element  102  to collapse completely and to seal off all air flow through the flow governor  101 . 
     The point at which the tubular element  102  collapses and the flow rate at which the flow governor governs are dependent on the geometry of the internal support structure  103  (and particularly, on the cross-sectional area of the pillar lumens  110 ), and the properties of the tubular element  102 , in particular its wall thickness, air inlet cross sectional area, width, length and Shore hardness. For the tubular element  102 , material that has a low adhesive characteristic can also be preferable, to ensure a smooth transition from the collapsed to the open state by prevention of adhesion to a housing wall of an inhaler in which the flow governor  101  is positioned and/or to the internal support structure  103 . 
     As described in greater detail in the Examples section, mathematical modeling of flow governors of the type shown in  FIGS. 3-8  has demonstrated that the flow governors of one embodiment of the present invention are capable of governing at an air flow of 30 L/min. with a repeatability and consistency of ±5 L/min. over a wide range of patient pressure drops. Almost all patients, even those with very weak lungs, should be capable of achieving such air flow rates, yet because of the operation of the flow governor, no patients are likely to be able to exceed such air flow rates, even with very excessive effort. 
     Other arrangements of the embodiment described, such as the shape, size, number and location of elements belonging to the internal support structure, will be apparent to one skilled in the art. 
     Other designs or configurations of the internal support structure may be used instead of the hollow pillar and cross member arrangement of  FIGS. 3-8 . For example,  FIGS. 9-14  illustrate various flow governors of the present disclosure, wherein like numerals represent like elements.  FIGS. 9-13  illustrate a flow governor  201  according to another embodiment of the present disclosure that employs a different internal support structure; and  FIG. 14  illustrates a flow governor  301  according to yet another embodiment of the present disclosure. The flow governors of  FIGS. 9-14  share many of the same elements, features, and functions as the flow governor  101  of  FIGS. 3-8 . Reference is made to the description above accompanying  FIGS. 3-8  for a more complete description of the features and elements (and alternatives to such features and elements) of the embodiments illustrated in  FIGS. 9-14 . Any of the features described above with respect to  FIGS. 3-8  can be applied to the embodiments of  FIGS. 9-14 , and vice versa. 
     With reference to  FIGS. 9-13 , the flow governor  201  includes a tubular element  202  comprising at least one flexible wall  240 , and an internal support structure  203 . In this embodiment, the internal support structure  203  includes a hollow base  204 , solid pillars  205  (i.e., with no lumens), a cross member  206 , and one or more splines (or transverse protrusions or transverse splines)  213  (see  FIGS. 10 and 12 ) protruding from the cross member  206  (e.g., protruding transversely from the laterally oriented cross member  206 ). In some embodiments, as shown, the one or more transverse protrusions  213  can be located laterally centrally with respect to the internal support structure  203  and protruding forwardly and rearwardly with respect to the cross member  206  (i.e., when viewed in transverse cross-section, as shown in  FIG. 10 ). In some embodiments, the one or more transverse protrusions  213  can protrude from the internal support structure  203  substantially orthogonally with respect to the at least one flexible wall  240  of the tubular element  202 . 
     By way of example only, the internal support structure  203  has an “H” shaped longitudinal cross-sectional shape (i.e., taken along the longitudinal direction D), as shown in  FIG. 9  and a generally “H” shaped transverse cross-sectional shape (i.e., taken substantially orthogonally with respect to the longitudinal direction D, e.g., in a lateral-transverse plane), as shown in  FIGS. 10 and 12 . 
     Furthermore, in embodiments employing at least one transverse protrusion  213 , the internal support structure  203  can further include a transverse cross-sectional shape including at least one capital English letter “E.” Particularly, in embodiments employing two laterally-centered transverse protrusions  213 , as shown in  FIGS. 10 and 12 , the internal support structure  203  can have a transverse cross-sectional shape including two capital letter “E”s, merged back-to-back and oriented with the long side of the “E” in the lateral direction L. Unlike the hollow pillars  105  of  FIGS. 3-8 , the solid pillars  205  lack any internal lumen with long aspect ratios, and therefore have a geometry that may be more desirable for ease of manufacture. Other arrangements, not necessarily “H”-shaped in longitudinal or transverse cross-section, will also be apparent to one skilled in the art. Examples include flow governors having one or more internal support structures having transverse cross-sectional shapes including, or similar to, any of the letters selected from the English capital letters of B, C, D, E, H, M, N, O, S, V, W, X and Z. Other shapes will also be apparent to one of ordinary skill in the art. 
       FIGS. 9-11  illustrate the flow governor  201  at rest (i.e., with the tubular element  202  in an uncollapsed state), and  FIGS. 12-13  illustrate the flow governor  201  in an operative state (i.e., with the tubular element  202  in a collapsed state). 
     The flow governor  201  includes an air flow path  207  formed between the internal support structure  203  and the tubular element  202 , the air flow path  207  including an air inlet  208  and air outlet  209 .  FIG. 10  shows a transverse cross-section of the flow governor  201 , taken generally perpendicularly with respect to the general direction of air flow, which illustrates that the tubular element  202  has an approximately elliptical transverse cross-sectional shape at rest. In some embodiments, as shown, the splines  213  protrude outwardly from the cross member  206  (e.g., in the transverse direction T) less than the solid pillars  205  do. In alternative embodiments, the splines can be dimensioned to protrude an equal distance from the cross member  206  as the solid pillars  205 , or alternatively, can protrude further. Alternatively, each solid pillar  205  can have a transverse cross-sectional shape in the form of a cross rather than an approximate rectangle. Many more variants to the cross-sectional shape and dimensions of the internal support structure  203  are possible, as will be apparent from these examples. Each variant will have its own air flow characteristics as a function of pressure drop and air flow rate, in combination with the characteristics of the form and material of the tubular element  202 . 
       FIG. 11  illustrates that the tubular element  202  and the solid pillars  205  are oriented generally parallel to the longitudinal direction D, and that the tubular element  202  is not in contact with the solid pillars  205  at rest, and that the pillars protrude from the tubular element  202  at the air inlet  208  (i.e. protrude from an upstream end of the tubular element  202 . 
       FIGS. 12 and 13  illustrate the flow governor  201  in an operative state. When air is sucked through the air outlet  209 , it flows into the air flow path  207  via the air inlet  208 . As shown, the reduced air pressure created by the patient&#39;s inhalation causes a reduction in diameter along the minor axis of the elliptically sectioned tubular element  202  resulting in inward bending as shown in  FIG. 12 . As the tubular element  202  is supported at the downstream end by the hollow base  204 , inward bending occurs predominantly at the end of the tubular element  202  that is nearer to the air inlet  208 , the inward bending restricting the cross-sectional area of the air flow path  207 . The lower the air pressure in the air flow channel  207 , the greater the inward deformation of the tubular element  202  and hence, the greater the reduction in the cross-sectional area of the air flow path  207  and the greater the resistance to air flow. 
     Complete collapse of the elliptical cross-sectioned tubular element  202  is prevented by the solid pillars  205 . These structures, along with the cross member  206 , provide structural support that prevents significant reduction in the diameter along the major axis of the elliptically sectioned tubular element  202 . The splines  213  additionally provide support along the minor axis, preventing the tubular element  202  (and particularly, the at least one flexible wall  240 ) from collapsing too tightly onto the cross member  206 . Residual air flow is thus always possible via the residual air flow channel gaps, no matter how great the patient&#39;s inspiratory pressure drop. 
       FIG. 14  illustrates a flow governor  301  according to another embodiment of the present disclosure. The flow governor  301  includes a tubular element (or “tube”)  302  comprising at least one flexible wall  340 , and an internal support structure  303  that is dimensioned to be received within the tubular element  302  (i.e., within the at least one flexible wall  340 ). The tubular element  302  surrounds and envelopes the internal support structure  303 . The internal support structure  303  consists of a hollow base  304 , two hollow pillars  305  (each comprising a lumen  310 ), and a cross member  306 . As shown in  FIG. 14 , in some embodiments, the tubular element  302  can be anchored or otherwise attached (e.g., to the internal support structure  303 ) at both ends, rather than being free at the air inlet end. As shown in  FIG. 14 , in some embodiments, the cross member  306  can be located longitudinally centrally with respect to the pillars  305 . As a result, in addition to the lateral and transverse symmetries of previous embodiments, the internal support structure  303  (and the flow governor  301 ) can also have longitudinal symmetry (e.g., about a central lateral-transverse plane). 
     As with previous embodiments, the outer diameter of the hollow base  304  is larger than the inner diameter of the flexible tubular element  302 , and assembly of the two components is achieved by stretching the tubular element  302  over the outer surface of the hollow base  304 . The tubular element  302  and the internal support structure  303  together define an air flow path  307  therebetween that includes an air inlet  308  and an air outlet  309 . The air flow path  307  also includes the lumens  310  through the pillars  305 . When air is sucked towards the air outlet  309 , it flows into the air flow path  307  and through (i.e., via) the lumens  310  and around the pillars  305  via the air inlet  308 , creating a reduction in air pressure in the air flow path  307  by the Bernoulli Effect. The reduced pressure in the air flow path  307  causes a reduction in the diameter along the minor axis of the elliptical cross-section of the tubular element  302  centered at approximately the midpoint of the air flow path  307 . 
     One possible advantage of having the tubular element  302  secured at both ends is that the tubular element  302  can be of greater thickness for a given flow governing performance, thereby offering a manufacturing advantage with regard to the dimensional specification range of the tubular element  302 . Another possible advantage of having the tubular element  302  secured at both ends is that the use of a symmetrical arrangement (e.g., symmetrical longitudinally, laterally and transversely) can offer a manufacturing benefit, as it does not require a consistent and specified end-to-end orientation during assembly. 
       FIGS. 26 and 27  illustrate a flow governor  1001  according to another embodiment of the present disclosure that employs a different internal support structure. The flow governor of  FIGS. 26 and 27  shares many of the same elements, features, and functions as the flow governors of  FIGS. 3-14 . Reference is made to the description above accompanying  FIGS. 3-14  for a more complete description of the features and elements (and alternatives to such features and elements) of the embodiment illustrated in  FIGS. 26 and 27 . Any of the features described above with respect to  FIGS. 3-14  can be applied to the embodiment of  FIGS. 26 and 27 , and vice versa. 
     With reference to  FIG. 26 , a side cross-sectional view of the flow governor  1001  including a tubular element  1002  comprising at least one flexible wall  1040  and an internal support structure  1003  is shown. In this embodiment, the internal support structure  1003  includes a hollow base  1004 , solid pillars  1005  (i.e., with no lumens), and a cross member  1006 . In this embodiment, the tubular element  1002  runs substantially parallel to the solid pillars  1005 , but is not in contact with them. 
     At the air inlet  1008 , the solid pillars  1005  protrude from the tubular element  1002 . In addition, the cross member  1006  is located outside the tubular element  1002  at the air inlet  1008 . In  FIG. 26 , the cross member  1006  is positioned at the ends of the solid pillars  1005 . In some embodiments, the cross member may be positioned some distance from the ends of the pillars, provided the cross member is located outside the tubular element. 
     By way of example only, the internal support structure  1003  has an inverted “U” shaped longitudinal cross-sectional shape when viewed in front longitudinal cross-section view, as shown in  FIG. 26  and a generally “H” shaped transverse cross-sectional shape (i.e., when viewed substantially orthogonally with respect to the longitudinal direction D, e.g., in a lateral-transverse plane), as shown in  FIG. 27 . 
     Any of the various alternatives for the designs of the pillars and cross members described herein may be used. Two such exemplary embodiments are illustrated in  FIG. 28 . As shown in  FIG. 28A , an internal support  1023  includes a cross member  1026  connected to two pillars  1025 , which are hollow such that they include lumens  1020 . Alternatively, as shown in  FIG. 28B , a cross member  1016  may be generally “O” shaped (e.g., circular or elliptical). Such a cross member may be mounted between or on top of pillars (not shown) to form the support structure. 
     If the cross member is located inside the tubular element, the cross member will contribute to the overall flow restriction and the resulting flow rates and pressure drops. By locating the cross member outside the tubular element beyond its upstream end, the cross member can still contribute to the structural integrity of the support structure without blocking any portion of the interior of the tubular element. As a result, by locating the cross member outside the tubular element, lower initial resistances and higher average flow rates may be achieved compared to similar support structures where the cross member is located within the tubular element. 
     Medicinal Inhalers 
       FIG. 15  illustrates a medicinal inhaler  250  according to one embodiment of the present disclosure that employs a flow governor  101  of the present disclosure. By way of example only, the medicinal inhaler  250  is shown in  FIG. 15  as including the flow governor  101  of  FIGS. 3-8 ; however, it should be understood that any flow governor of the present disclosure can be employed in the inhaler  250 . By way of further example, the medicinal inhaler  250  is shown as being a press-and-breathe pressurized metered dose inhaler (pMDI). 
     The inhaler  250  shares many of the elements, features, and functions of the pMDI  50  of  FIG. 1 , wherein like numerals represent like elements. As a result, reference is made to the description above accompanying  FIG. 1  for a more complete description of the features and elements (and alternatives to such features and elements) of the inhaler  250  of  FIG. 15 . 
     The inhaler  250  includes a canister  251  containing a medicament formulation  252 , the canister comprising a can  253  sealed with a metering valve  254 . The canister  251  sits within a housing (or “actuator”)  255  comprising an initially open tubular sleeve portion  256  having a first open end  247  dimensioned to receive the canister  251  and from which its base  249  can protrude, and a portion in the form of an open tubular mouthpiece  257 . The open housing  255  can define an air flow path  246  therein, in particular from an air inlet  215 , open to ambience, to the mouthpiece  257  that defines an inhalation orifice or an air outlet  245 . A stem portion  258  protrudes from the metering valve  254  and is located and retained by friction in a stem socket  259  formed as an integral part of the housing  255 . A spray orifice  260  is formed in the stem socket  259 , and provides a passage for fluid communication between the valve stem portion  258  and the mouthpiece  257 . 
     As further shown in  FIG. 15 , the inhaler  250  further includes the flow governor  101  incorporated directly into the inhaler  250  by being positioned in the air flow path  246  of the inhaler  250 . Particularly, in the embodiment of  FIG. 15 , the flow governor  101  is located in a dedicated tubular air flow path  214  between the air inlet  215  and an air outlet  216  in fluid communication with the air outlet  245  of the inhaler  250 , such that the air flow path  214  forms a portion of the overall air flow path  246  of the inhaler  250 . 
     By way of example only, the dedicated air flow path  214  is located at a rear portion of the housing  255  (i.e., opposite the mouthpiece  257 ) and is integrally formed with the housing  255 . By way of further example, the air inlet  215  is defined by a second open end  220  of the housing  255 , wherein the second open end  220  is dimensioned to receive the flow governor  101 . As a patient inhales on the mouthpiece  257 , air flows via the air inlet  215  into the flow governor  101 , creating the reduced pressure required to activate the flow governor  101 , thus regulating the air flow. In order to avoid any ingress of air from the top of the inhaler  250  that would bypass the flow governor  101 , a cover  217  that forms a seal is located over the first open end  247  of the housing  255 . The cover  217  can be flexible, in order to allow the base  249  of the canister  251  to still be depressed to deliver the dose of medicament formulation. This flexibility can be provided via appropriate choice of material(s) of manufacture for the cover  217 , via the cover geometry and design, or both. 
     The dedicated air flow path  214  is shown as being substantially constant in cross section in  FIG. 15 ; however, this need not be the case. Various possible shapes and configurations for air flow paths including a flow governor of the present disclosure and for being incorporated into a medicinal inhaler of the present disclosure are described in greater detail below with reference to  FIGS. 20-23 . 
       FIG. 16  illustrates a medicinal inhaler  350  according to another embodiment of the present disclosure. The inhaler  350  shares many of the elements, features, and functions of the inhalers  50  and  250  of  FIGS. 1 and 15 , respectively, wherein like numerals represent like elements. As a result, reference is made to the description above accompanying  FIGS. 1 and 15  for a more complete description of the features and elements (and alternatives to such features and elements) of the inhaler  350  of  FIG. 16 . 
     The inhaler  350  includes a housing  355  that defines an air flow path  346  therethrough, including an open end  320  and an air outlet  345  (formed by a mouthpiece  357 ). The housing  355  also includes an initially open tubular sleeve portion  356  having an open end  347  dimensioned to receive a canister  351  comprising a medicament formulation  352 . The inhaler  350  further includes the flow governor  101  (i.e., by way of example only) positioned in the air flow path  346  extending from the open end  320  to the air outlet  345 . Particularly, similar to the embodiment of  FIG. 15 , the flow governor  101  is positioned in a dedicated air flow path  314  that is open to ambience (e.g., via the open end  320 ) and in fluid communication with, and forms a portion of, the overall air flow path  346  of the inhaler  350 . In addition, the dedicated air flow path  314  is integrally formed with the housing  355 , and particularly is formed in a rear portion of the housing  355 , i.e., opposite the mouthpiece  357 . 
       FIG. 16  illustrates an alternative system for sealing the open end  347  of the housing  355  of the inhaler  350  to avoid bypass air ‘defeating’ the flow governor  101 . In this embodiment, a skirt seal  318  is used to seal or substantially seal the gap around the canister  351 . That is, the skirt seal  318  is located between an outer surface  322  of the canister  351  (and particularly, an outer surface  322  of a can  353  of the canister  351 ) and an inner surface  324  of the housing  355  (and particularly, an inner surface  324  of the sleeve portion  356  of the housing  355 ) to seal the open end  347  (i.e., the sleeve portion  356  of the housing  355 ) from ambience. 
     The skirt seal  318  can be formed of a thin and flexible annular elastomer and can be made sufficiently flexible to avoid introducing any great resistance to longitudinal canister movement in the sleeve portion  356  of the housing  355 . Other arrangements of sealing components will be apparent to one skilled in the art. 
       FIG. 17  illustrates a medicinal inhaler  450  according to another embodiment of the present disclosure. The inhaler  450  shares many of the elements, features, and functions of the inhalers  50  and  250  of  FIGS. 1 and 15 , respectively, wherein like numerals represent like elements. As a result, reference is made to the description above accompanying  FIGS. 1 and 15  for a more complete description of the features and elements (and alternatives to such features and elements) of the inhaler  450  of  FIG. 17 . 
     The inhaler  450  includes a housing  455  that defines an air flow path  446  therethrough, including an air passage  469  and an air outlet  445 . Particularly, the housing  455  includes an open tubular sleeve portion  456  having an initially open end  447  that defines the air passage  469 , and a mouthpiece  457  that defines the air outlet  445 . The sleeve portion  456  and the open end  447  are dimensioned to receive a canister  451  comprising a medicament formulation  452 . The inhaler  450  further includes the flow governor  101  (i.e., by way of example only) positioned in the air flow path  446 . 
       FIG. 17  illustrates another alternative system for sealing the open end  447  of the housing  455  of the inhaler  450  to avoid bypass air ‘defeating’ the flow governor  101 . In this embodiment, rather than having the flow governor  101 , or a dedicated air flow path, form a portion of or be built into the housing  455  of the inhaler  450 , the flow governor  101  is located in a cap  426  configured to be coupled to (e.g., clipped or snapped onto) the initially open end  447  of the housing  455  to close and seal the open end  447 , such that the cap  426  ends up forming a portion of the air flow path  446  when coupled to the housing  455 . As a result, the cap  426 , when coupled to the housing  455 , defines the air inlet of the air flow path  446  of the inhaler  450 , such that inhaled air must pass through the flow governor  101  in the cap  426 . In this embodiment, the cap  426  can be provided as a retro-fitted accessory to an existing inhaler. 
     Similar to the cover  217  of  FIG. 15 , the cap  426  can be formed of a flexible material to allow the canister  451  to still be pressed when desired. In addition, or alternatively, as shown in  FIG. 17 , in some embodiments, the inhaler  450  can include a button  419  to allow the canister  451  to be pressed to release a dose of medicament. For example, in some embodiments, the button  419  can be fixed with respect to the cap  426 , and the cap  426  can be flexible. In some embodiments, the cap  426  need not be flexible, and the button  419  can be movable with respect to the cap  426 . 
     In other embodiments, the flow governors of the present disclosure can be built into other locations within an inhaler. For example, the flow governor could be positioned below the foot of the stem socket (see, e.g., the stem socket  59  of  FIG. 1 ) into which the valve stem portion (see, e.g., the stem portion  58  of  FIG. 1 ) of the canister (see, e.g., the canister  51  of  FIG. 1 ) locates. In such embodiments, e.g., its inlet can be positioned below the mouthpiece of the inhaler (see, e.g., the mouthpiece  57  of  FIG. 1 ), and its outlet could be arranged to feed air to the stem socket region. A sealing cover (see, e.g., the cover  217  of  FIG. 15 ), a skirt seal (see, e.g., the skirt seal  318  of  FIG. 16 ), or another sealing means can be employed over the open end of the housing that receives the canister of medicament to avoid any air bypassing the flow governor. 
     In any of the inhalers of the present disclosure employing flow governors of the present disclosure, grill structures can be provided over the air inlet of the air flow path in which the flow governor is located, such that large pieces of debris, for example, are not inadvertently taken into the inhaler device. Furthermore, in each embodiment of the inhaler of the present disclosure, the air inlet of the flow governor air flow path is preferably positioned where it will not readily be inadvertently blocked or obstructed by a patient&#39;s lips, fingers, etc., during use. 
       FIG. 18  illustrates a medicinal inhaler  550  according to another embodiment of the present disclosure. By way of example only, the inhaler  550  is substantially the same as the inhaler  250  of  FIG. 15  and includes the flow governor  101  positioned in the air flow path  546  of the inhaler, except that the inhaler  550  further includes one or more pressure sensors  525 ,  527  located in the dedicated flow governor air flow path  514 . Reference is made to the description above accompanying  FIG. 15  for a more complete description of the features and elements (and alternatives to such features and elements) of the inhaler  550  of  FIG. 18 . 
     As shown in  FIG. 18 , a pressure sensor  525  is located in fluid communication with the dedicated air flow path  514 . The pressure sensor  525  is connected to a controller (not shown), both of which are powered by a suitable power source (not shown) with an appropriate switch to provide a power on/off function. 
     Generally, a controller of the present disclosure can be a suitable electronic device, such as, for example, a programmable logic controller (“PLC”), a programmable circuit board (“PCB”), a microprocessor, and/or other suitable devices or structures. As such, the controller  151  may include both hardware and software components, and the term “controller” is meant to broadly encompass the combination of such components. 
     With continued reference to  FIG. 18 , when the power is switched on, the pressure sensor  525  determines the atmospheric pressure. When the patient inhales air through the inhaler  550 , causing air to flow out of the air outlet  516 , air flows into the air flow path  514  via the air inlet  515 , and the pressure sensor  525  detects and/or measures the dynamically changing air pressure brought about by the patient&#39;s inspiratory effort in conjunction with the functionality of the flow governor  101 . 
     Detection of pressure changes, relative to the initial atmospheric pressure, via cooperation between the pressure sensor  525  and a controller, can be used to calculate the air flow rate past the pressure sensor  525 . (The air flow rate causes a reduction in local air pressure, via the Bernoulli Effect.) When a desired pre-determined flow rate is reached, an electronic signal can be sent to a suitable component, such as a Light Emitting Diode (LED) or Liquid Crystal Display (LCD) or audio speaker, to provide a cue for the user to actuate the inhaler  550 . Alternatively, the electronic signal could be used to enable a mechanism to automatically actuate the inhaler  550 . 
     Furthermore, in some embodiments, a second pressure sensor  527  can be included in the air flow path  514  towards the air outlet  516 . The presence of this second pressure sensor  527  can be used to determine air flow direction via comparison (e.g., performed by the controller) of the relative local air pressures at the two pressure sensors  525 ,  527 , which can be used to distinguish inspiration from exhalation (e.g., if a patient blows into the inhaler  550  instead of sucking air through the inhaler  550 ). This can allow a linked breath-actuation triggering mechanism (e.g., mechanical or electronic) to be arranged not to operate if the patient breathes out into the inhaler, rather than in through it, the two breathing modes being easily differentiated by the different relative pressure drop relationships detected by the first and second sensors  525  and  527 . 
     Inclusion of two pressure sensors  525 ,  527  in fluid communication with the air flow path  514  enables measurement (in conjunction with the appropriate electrical components, such as a controller (e.g., a programmable circuit board (PCB)), a power source, etc.) of pressure changes, which can be correlated with air flow rates. When a predetermined flow rate is achieved, this can prompt a signal to trigger an electrical firing mechanism to actuate the inhaler canister  551 . Such a mechanism can negate the requirement for the patient to coordinate inhaling and actuating the inhaler. In addition, the triggering flow rate can be programmed differently for different products. 
     In each case, though, use of an integral flowmeter (which the pressure sensors  525 ,  527  can effectively be) and electronic actuation can ensure that the inhaler  550  can be actuated at an appropriate time in the patient&#39;s inspiratory maneuver. The electronic circuitry involved can also be configured to allow each triggering event to be counted and recorded, and can be used to also provide a dose count, e.g. for display to the patient of the theoretical number of doses thus still remaining. 
     As well as using the pressure measurements and the calculated flow rate data to trigger canister actuation, such a system can optionally be configured to provide feedback to the patient and to their physician. 
     The air flow path  514  containing the flow governor  101  can be incorporated, in a similar fashion as already described, into any of the variety of inhalers mentioned above. It should also be understood that the incorporation of pressure sensors in the flow governor air flow path can be employed in any inhaler, such as that of any of  FIGS. 15-17 , or any other inhaler of the present disclosure. By way of example, the pressure sensors of  FIG. 18  can be positioned in an air flow path formed in the cap  426  of  FIG. 17 . The relevant electronic componentry can also be incorporated into the cap  426 . 
     In some embodiments, no matter which type of inhaler is employed, the air flow path  514  including the flow governor  101  and the pressure sensors  525 ,  527 , along with the relevant electrical components, can be manufactured as a separate part or component, or as a portion of the inhaler  550 .  FIGS. 20-23 , described below, illustrate exemplary flow governor assemblies (or “air flow paths” or “air flow path assemblies”) of the present disclosure comprising flow governors of the present disclosure that can be separately formed and put in fluid communication with or otherwise incorporated into an inhaler, or that can form a portion of an inhaler of the present disclosure. 
       FIG. 19  illustrates an inhaler  750  according to another embodiment of the present disclosure, including the flow governor  101  of  FIGS. 3-8 . By way of example, the inhaler  750  is illustrated as being a variant of an inhaler available under the trade designation AUTOHALER™ from 3M Company, St. Paul, Minn. Additional details regarding the inhaler  750  can be found in U.S. Pat. No. 7,296,567, which is incorporated herein by reference in its entirety. 
     As shown in  FIG. 19 , the flow governor  101  is positioned in a dedicated air flow path  714  located in a bottom portion of a housing  755  of the inhaler  750 , which is integrally formed with the housing  755 . The dedicated air flow path  714  includes an air inlet  715  (e.g., defined by an auxiliary open end  720 ) open to ambience and an air outlet  716  in fluid communication with an air flow path  746  of the inhaler  750 . Particularly, the dedicated air flow path  714  is arranged substantially horizontally, such that the air inlet  715  is located generally below the mouthpiece  757 . Sealing means (not shown) are provided to ensure that there are no significant air leak inlets elsewhere in the inhaler  750 , in order that substantially all the air flow through the inhaler  750  passes through the dedicated air flow path  714 . 
     In this embodiment, the inspiratory air flow is drawn via the air inlet  715  (e.g., via an inlet grill, screen or grate  728 ) into the flow governor  101  and thence into the region around a stem socket  759 . When the patient inhales on the mouthpiece  757  of the inhaler  750  (which defines an inspiration orifice  745 ), a vane  777  lifts in the inspiratory air flow, that lifting triggering a mechanical dose release mechanism  728 . The emerging medicament formulation spray  761  is entrained in the air flow from the air outlet  709  of the flow governor  101  and the air outlet  716  of the dedicated air flow path  714  and emerges with the air flow via the mouthpiece  757 . It will be noted by one skilled in the art that flow governors of the present invention may be positioned in multiple locations in such an inhaler, e.g. at the rear of the inhaler, at the front, on the top, to one side, etc. Additionally, it will be apparent that the outer form of the inhaler can be shaped and styled independently of the internal air flow surfaces. 
     Again, incorporation of an appropriate electronic memory device could allow capture, storage and retrieval of the patient&#39;s inhalation profile (flow rates, pressure drops, etc.) corresponding to each time the inhaler was used. Inclusion of a means to transmit the data, e.g. via a cable or using wireless technology, to a secondary device, e.g. a computer or ‘smart’ phone, could make these data readily available to the patient&#39;s physician or others, in order to allow them to monitor the patient&#39;s ability to use the inhaler successfully and to allow appropriate and timely health care advice to be provided based on analysis and interpretation of the retrieved information. 
     In alternative embodiments, the breath-actuated inhaler can include both a reusable and a replaceable part. For example, a reusable part containing the complex and relatively expensive electronics could be paired in turn with a series of replaceable medicament containing cartridges. 
     In such embodiments, the flow governor can be associated with the replaceable cartridge or, alternatively and preferably, with the reusable unit. In either case, the air flow path of the inhaler can be configured to pass through either the reusable part, the replaceable refill part, or both. 
     In yet another embodiment, two or more flow governors with differing resistances and/or collapse characteristics can be incorporated into a medicinal inhaler of the present disclosure, or an air flow path of the present disclosure for use with a medicinal inhaler, for example, in a parallel flow path configuration. In a still further embodiment, two or more flow governors with differing resistances and/or collapse characteristics can be incorporated into a medicinal inhaler or air flow path of the present disclosure in a series flow path arrangement. Such embodiments can provide a greater ability to adjust the flow rate versus pressure drop characteristics of medicinal inhalers. 
     Flow Governor Assemblies 
       FIG. 20  illustrates a flow governor assembly (or “air flow path” or “air flow path assembly”)  630  according to one embodiment of the present disclosure. The flow governor assembly  630  can be separately formed and put in fluid communication with or otherwise incorporated into an inhaler, or can form a portion of an inhaler of the present disclosure. As shown in  FIG. 20 , the flow governor assembly  630  can include a housing  635  that defines an air flow path  614  comprising an air inlet  615  and an air outlet  616 ; a flow governor  101  positioned in an air flow path  614 ; and a constriction  623  in the air flow path  614 . The housing  635  is shown in greater detail in  FIG. 21  and described in greater detail below. 
     The flow governor  101  can be configured to provide a variable (dynamic) resistance to air flow in an air flow path  614 ; and the constriction  623  can be configured to provide a fixed (static) resistance to air flow in the air flow path  614 . The constriction  623  can include one or more of a venturi section (as shown), a narrow passageway (e.g., a narrow passageway, relative to adjacent regions/portions of the air flow path  614 ), a tortuous path, and a combination thereof. A tortuous path can include one or more twists, bends or turns (e.g., a sharp turn of at least 60 degrees). 
     In addition, in some embodiments, the flow governor assembly  630  can further include a first (air inlet) pressure sensor  625 , and a second (air outlet) pressure sensor  627 . The flow governor assembly  630  can be of dimensions (e.g., a length) appropriate to the physical dimensions of an associated inhaler. 
     In some embodiments, the housing  635  can be a separate element that can be positioned within, positioned in fluid communication with, and/or coupled to a housing of an inhaler. Additionally, or alternatively, in some embodiments, the housing  635  can refer to a portion of a housing of an inhaler, such that the housing  635  is integrally formed with a housing of an inhaler. 
     The air flow path  614 , and particularly, the air inlet  615  can be shaped to improve the sensitivity of at least the first pressure sensor  625 . The first pressure sensor  625  is connected to the air flow path  614  by a first conduit  621 . The dimensions of this conduit (e.g., its cross-sectional area) can be chosen to ensure an appropriate balance between having a desirably low pressure drop along its length versus avoiding it being open enough to significantly affect the air flow in the main air flow path  614 . In some embodiments, this conduit can be round in cross-section, with an internal diameter of approximately 2 mm and a total internal length of approximately 15 mm. 
     As mentioned above, the air flow path  614  can further include a fixed or static resistance, particularly, in the form of a constriction (or “venturi constriction”)  623  located between the air inlet  615  and the air outlet  616  that particularly forms a venturi tube (or venturi section) that effectively amplifies the local air flow induced pressure drop at the first pressure sensor  625 . 
     Particularly, the constriction  623  can be located upstream of the flow governor  101 . Such an amplification can enable the use of a less sensitive pressure sensor to measure the air flow rate with a given accuracy. This helps to constrain the manufacturing cost of the inhaler into which the assembly  630  is incorporated. 
     Addition of the second pressure sensor  627  connected by a second conduit  629  (e.g., in some embodiments, having an internal diameter of approximately 2 mm and an internal length of approximately 9 mm), to the air flow path  614  at a position downstream of, and away from, the venturi section constriction  623  can assist in determining the air flow direction (i.e., to distinguish inhalation from exhalation). This allows a linked breath-actuation triggering mechanism (e.g., mechanical or electronic) to be arranged not to operate if the patient breathes out into the inhaler, rather than in through it, the two breathing modes being easily differentiated by the different relative pressure drop relationships detected by the first and second sensors  625  and  627 . 
     In some embodiments, the first conduit  621  can have a first cross-sectional area (e.g., an average cross-sectional area, or a cross-sectional area in a region of the first conduit located adjacent the first pressure sensor); the second conduit  629  can have a second cross-sectional area (e.g., an average cross-sectional area, or a cross-sectional area in a region of the first conduit located adjacent the first pressure sensor); and the air flow path  614  can have a third cross-sectional area (e.g., an average cross-sectional area, or a cross-sectional area in a region of the first conduit or the second conduit). 
     In some embodiments, the ratio of the first cross-sectional area to the third cross-sectional area and/or the ratio of the second cross-sectional area to the third cross-sectional area can be no greater than 0.3; in some embodiments, no greater than 0.25; in some embodiments, no greater than 0.2; in some embodiments, no greater than 0.18; in some embodiments, no greater than 0.16; in some embodiments, no greater than 0.15; in some embodiments, no greater than 0.1; in some embodiments, no greater than 0.08; in some embodiments, no greater than 0.07; and in some embodiments, no greater than 0.05. 
     The present inventors calculated that, in some embodiments, an inhaler comprising the flow governor assembly  630  of  FIG. 20  can provide an overall resistance to air flow at 20 L/min. (below the collapse flow rate) of around 0.8 Pa 0.5  min./L. This is a desirable figure for an inhaler for the treatment of either COPD or asthma. Computational Fluid Dynamics (CFD) is a useful tool for use by one skilled in the art to develop appropriately modified and dimensioned alternative embodiments to those shown herein. 
     In some embodiments, where an inhaler incorporates one or more pressure sensors, the patient&#39;s inhalation profile can be recorded for each use of the inhaler. With inclusion of the appropriate electronic components, e.g. a memory device and data transmission means, each inhalation profile of the patient can be captured, stored and retrieved for future analysis and interpretation. This can allow the patient&#39;s physician and others to monitor the patient&#39;s ability to use the inhaler successfully and can allow appropriate and timely health care advice and/or interventions to be provided. 
     Furthermore, in some embodiments, air flow pressure drop measurements can be made to enable an inhaler to register both the fact that a dose was taken and to record the corresponding inhalation profile. This enables the patient&#39;s physician, or an authority or organization paying for the patient&#39;s health care provision, to know that the patient has actually taken the dose. Previous inhalers that have registered the release of a dose, even with a record of the date and time of that release, have not registered or recorded the corresponding inhalation profile, making them vulnerable to ‘dose dumping’, a practice in which patients can deceive their physicians and others into thinking that they are taking their prescribed doses even when in fact they are simply wasting them by spraying the doses into the surrounding air, etc. Such practices are well known as occurring where patients are embarrassed to tell their physician that they have not been following their prescribed treatment regime. The ability to detect such practices, via utilization of embodiments of the present disclosure, allows health care professionals the opportunity to understand what patients are actually doing, and allows them to advise and/or alter treatment regimes accordingly. 
       FIG. 21  illustrates one example of the elements or components that can be used to make the flow governor assembly  630  of  FIG. 20 . For example, in some embodiments, a controller  632  (e.g., a programmable circuit board (PCB)) can include the two pressure sensors  625 ,  627 . As shown in  FIGS. 20-21 , the flow governor  101  comprises the tubular element  102  and the internal support structure  103 . The air flow path  614  can be formed by a housing  635 , which is shown as including a front housing  633  and a rear housing  634 , e.g., for ease of plastic injection molding that can be coupled together (e.g., via any of the coupling means described above with respect to coupling the tubular element  102  and the internal support structure  103 ). In some embodiments, the housing  635  can be formed by two or more longitudinal portions (i.e., as shown in  FIG. 21  by way of example), or additionally or alternatively, the housing  635  can be formed of two or more transverse portions that are joined transversely, relative to a longitudinal direction D, i.e., relative to the general air flow direction. The separate housing  635  is shown for simplicity and by way of example only; however, it should be understood that the assembly  630  and air flow path  614  can instead be formed (e.g., integrally formed) with a housing of a medicinal inhaler, and the inhaler can be modified to include all of the elements shown in  FIGS. 20-21  of the assembly  630 . 
     Various parameters affect the exact collapsing air flow rate and governing air flow rate for the flow governor  101  and the flow governor assembly  630 . Examples of such parameters include the material forming the tubular element  102 ; the diameter and thickness of the tubular element material; the shape and dimensions of the constriction  623  and of the internal support structure  103 ; and environmental factors such as temperature and humidity (e.g., depending on the tubular element material). Based on the teachings of the present disclosure, a person of ordinary skill in the art will recognize how to test the effects of varying these different input parameters without departing from the spirit and scope of the present invention, in order to optimize an exact configuration of flow governor and air flow path for a particular application. 
       FIG. 22  illustrates a flow governor assembly  830  according to another embodiment of the present disclosure. The flow governor assembly  830  can be separately formed and put in fluid communication with or otherwise incorporated into an inhaler, or can form a portion of an inhaler of the present disclosure. As shown in  FIG. 22 , the flow governor assembly  830  can include a flow governor  801  positioned in an air flow path  814 , the air flow path  814  including an air inlet  815  and an air outlet  816 . The air flow path  814  can be formed by a housing  835 . In some embodiments, the housing  835  can be a separate element that can be positioned within, positioned in fluid communication with, and/or coupled to a housing of an inhaler. Additionally, or alternatively, in some embodiments, the housing  835  can refer to a portion of a housing of an inhaler, such that the housing  835  is integrally formed with a housing of an inhaler. 
     The flow governor  801  includes a tubular element  802  and an internal support structure  803 . As shown in  FIG. 22  by way of example only, in some embodiments, the internal support structure  803  can include a hollow base  804  that can be at least partially formed by the housing  835 , or a portion thereof, such that the tubular element  802  is stretched externally around one portion (e.g., an outer wall) of the housing  835  and is located internally with respect to another portion of the housing  835 . In such embodiments, the entire internal support structure  803  can be integrally formed, or provided by, a portion of the housing  835 , which, as described above, can also form at least a portion of an inhaler. 
     As further shown in  FIG. 22 , the air flow path  814  can include (e.g., the housing  835  can include) one or more inwardly-projecting protrusions or features  837  positioned at one or more desired longitudinal positions to encourage the tubular element  802  of the flow governor  801  to collapse at specific, pre-defined locations. In some embodiments, the one or inwardly-projecting protrusions  837  can be in the form of pinching splines, or in some embodiments, the protrusion(s)  837  can include an annular protrusion surrounding the tubular element  802 . The protrusions(s)  837  can apply mechanical stress to the tubular element  802 . By altering the size and/or number of the protrusion(s)  837 , the flow rate at which the tubular element  802  collapses can be controlled. Additionally, or alternatively, in some embodiments, the tubular element material properties can be controlled to encourage precise collapse geometry and characteristics, e.g., by employing a particular Shore hardness at a specific section of the tubular element  802 . 
     The protrusion(s)  837  can also reduce any tendency of the inwardly flexing regions of the tubular element  802  to stick to the housing  835 , e.g. if the patient exhales moisture into the inhaler. 
     Furthermore, in some embodiments, the air flow path  814  can include a constriction, and particularly, a constriction located upstream of the flow governor  801 , i.e., toward the air inlet  815 , used as a venturi section to accelerate the local air velocity past an adjacent pressure sensor (not shown), as described above with respect to  FIGS. 20 and 21 . Such an arrangement can allow for more precise pressure measurements (and calculated air flow rate measurements) than would otherwise be achieved from a given pressure sensor. 
       FIG. 23  illustrates a flow governor assembly  930  according to another embodiment of the present disclosure. The flow governor assembly  930  can be separately formed and put in fluid communication with or otherwise incorporated into an inhaler, or can form a portion of an inhaler of the present disclosure. As shown in  FIG. 23 , the flow governor assembly  930  can include a flow governor  901  positioned in an air flow path  914 , the air flow path  914  including an air inlet  915  and an air outlet  916 . The air flow path  914  can be formed by a housing  935 . In some embodiments, the housing  935  can be a separate element that can be positioned within, positioned in fluid communication with, and/or coupled to a housing of an inhaler. Additionally, or alternatively, in some embodiments, the housing  935  can refer to a portion of a housing of an inhaler, such that the housing  935  is integrally formed with a housing of an inhaler. 
     The flow governor  901  includes a tubular element  902  and an internal support structure  903 . As shown in  FIG. 23  by way of example only, in some embodiments, the internal support structure  903  can include a hollow base  904  that can be at least partially formed by the housing  935 , or a portion thereof, such that the tubular element  902  is stretched externally around one portion of the housing  935  and is located internally with respect to another portion of the housing  935 . As shown, in some embodiments, the air flow path  914  can include a venturi constriction  923  upstream of the flow governor  901 , which can be used to enhance the sensitivity of an adjacent pressure sensor (not shown) as has already been described. 
     In some embodiments, as shown in  FIG. 23 , the air flow path  914  can include one or more features that can be directly formed in the housing  935  into which the flow governor  901  sits to direct the flowing air into the flow governor  901 . For example, as shown in  FIG. 23 , the air flow path  914  can include a channeling step  936  that directs the air flow into the flow governor  901  and prevents air flow to an outer, external, side of the tubular element  902 , thus preventing pressure drop loss and keeping the air on the outer surface of the tubular element  902  stagnant. 
     Each embodiment shown in the figures is illustrated as a separate embodiment for clarity in illustrating a variety of features of the flow governors and medicinal inhalers of the present disclosure. However, it should be understood that any combination of elements and features of any of the embodiments illustrated in the figures and described herein can be employed in the flow governors and medicinal inhalers of the present disclosure. For example, any of the features of the flow governor assemblies of  FIGS. 20-23 , or combinations thereof, or partial combinations thereof, can be incorporated into any of the medicinal inhalers of  FIGS. 15-19 . Furthermore, any of the flow governor features of  FIGS. 3-14 , or combinations thereof, or partial combinations thereof, can be incorporated into any of the flow governor assemblies or medicinal inhalers of the present disclosure. 
     The following embodiments are intended to be illustrative of the present disclosure and not limiting. 
     EMBODIMENTS 
     1. A flow governor for use in a medicinal inhaler, the flow governor comprising: 
     a tubular element that defines at least a portion of an air flow path, the tubular element comprising at least one flexible wall configured to flex inwardly in response to an air flow in the air flow path; and 
     an internal support structure, located within the tubular element and configured to preserve at least a predetermined cross-sectional area of the air flow path within the tubular element when the at least one flexible wall of the tubular element flexes inwardly. 
     2. The flow governor of embodiment 1, wherein the flow governor is substantially linear. 
     3. The flow governor of embodiment 1 or 2, wherein the tubular element is substantially bistable between an uncollapsed state and a collapsed state. 
     4. The flow governor of any of embodiments 1-3, wherein the internal support structure is rigid relative to the tubular element, and the tubular element is flexible relative to the internal support structure. 
     5. The flow governor of any of embodiments 1-4, further comprising a longitudinal direction, wherein the at least one flexible wall of the tubular element is oriented substantially parallel to the longitudinal direction. 
     6. The flow governor of embodiment 5, wherein the tubular element is elongated along in the longitudinal direction. 
     7. The flow governor of any of embodiments 1-6, further comprising: 
     an air inlet located at a first end of the tubular element; and 
     an air outlet located at a second end, opposite the first end, of the tubular element. 
     8. The flow governor of any of embodiments 1-7, wherein the flow governor has an elliptical transverse cross-sectional shape. 
     9. The flow governor of any of embodiments 1-8, wherein the tubular element has an elliptical transverse cross-sectional shape. 
     10. The flow governor of any of embodiments 1-9, wherein the internal support structure has a base having an outer wall, and wherein an end of the tubular element is stretched over the outer wall of the base of the internal support structure. 
     11. The flow governor of embodiment 10, wherein the outer wall of the base of the internal support structure has an elliptical transverse cross-sectional shape. 
     12. The flow governor of embodiment 10 or 11, wherein the outer wall of the base of the internal support structure has a circular transverse cross-sectional shape. 
     13. The flow governor of any of embodiments 1-12, wherein the internal support structure includes at least one hollow pillar, and wherein the air flow path through the flow governor includes a space between an outer wall of the internal support structure and the tubular element, and a space within the at least one hollow pillar. 
     14. The flow governor of any of embodiments 1-13, wherein the internal support structure has a generally H-shaped transverse cross-sectional shape. 
     15. The flow governor of any of embodiments 1-14, wherein the internal support structure has a generally H-shaped longitudinal cross-sectional shape. 
     16. The flow governor of any of embodiments 1-15, wherein the internal support structure includes a transverse cross-sectional shape comprising at least one capital English letter “E”. 
     17. The flow governor of any of embodiments 1-16, wherein the internal support structure includes a transverse cross-sectional shape comprising at least one of the capital English letters selected from B, C, D, E, H, M, N, O, S, V, W, X and Z. 
     18. The flow governor of any of embodiments 1-17, wherein the internal support structure includes at least one pillar oriented substantially along a longitudinal direction of the tubular element and protruding from an inlet end of the tubular element. 
     19. The flow governor of any of embodiments 1-18, wherein the internal support structure includes at least one hollow pillar defining a lumen therein. 
     20. The flow governor of any of embodiments 1-19, wherein the internal support structure includes at least one solid pillar. 
     21. The flow governor of any of embodiments 1-20, wherein the internal support structure includes two pillars oriented substantially parallel to a longitudinal direction of the tubular element, and a cross member positioned to couple the two pillars, the cross member oriented at a non-zero angle with respect to the longitudinal direction. 
     22. The flow governor of any of embodiments 1-21, wherein the internal support structure includes two hollow pillars oriented substantially parallel to a longitudinal direction of the tubular element, each pillar defining a lumen therein, and a solid cross member positioned to couple the two hollow pillars, the cross member oriented at a non-zero angle with respect to the longitudinal direction. 
     23. The flow governor of any of embodiments 1-21, wherein the internal support structure includes two solid pillars oriented substantially parallel to a longitudinal direction of the tubular element, and a solid cross member positioned to couple the two solid pillars, the cross member oriented at a non-zero angle with respect to the longitudinal direction. 
     24. The flow governor of any of embodiments 21, 22 and 23, wherein the internal support structure includes at least one transverse protrusion extending from the cross member. 
     25. The flow governor of any of embodiments 21-24, wherein the cross member is oriented substantially perpendicularly with respect to the longitudinal direction. 
     26. The flow governor of any of embodiments 1-25, wherein the internal support structure includes at least one rib that protrudes substantially orthogonally with respect to the at least one flexible wall of the tubular element. 
     27. A medicinal inhaler comprising at least one flow governor of any of the preceding embodiments positioned in fluid communication with an air flow path of the medicinal inhaler. 
     28. The medicinal inhaler of embodiment 27, wherein the medicinal inhaler includes at least two flow governors arranged in parallel. 
     29. The medicinal inhaler of embodiment 27 or 28, wherein the medicinal inhaler includes at least two flow governors arranged in series. 
     30. A medicinal inhaler comprising: 
     a housing comprising
         a tubular sleeve portion dimensioned to receive a canister comprising a medicament, and   a patient port;       

     an air flow path including an air inlet and an air outlet, wherein the air outlet is defined by the patient port; and 
     the flow governor of any of embodiments 1-26 positioned in the air flow path. 
     31. The medicinal inhaler of any of embodiments 27-30, wherein the medicinal inhaler is a pressurized metered dose inhaler (pMDI). 
     32. The medicinal inhaler of any of embodiments 27-30, wherein the medicinal inhaler is at least one of a breath-actuated inhaler, a pressurized metered dose inhaler (pMDI), a dry powder inhaler (DPI), a nebulizer, and a combination thereof. 
     33. The medicinal inhaler of any of embodiments 30-32, wherein the tubular sleeve portion of the housing includes a first open end, and wherein the housing further includes a second open end dimensioned to receive the flow governor. 
     34. The medicinal inhaler of embodiment 33, wherein the housing further includes a cover or a seal positioned to seal the first open end from ambience. 
     35. The medicinal inhaler of any of embodiments 27-34, wherein the flow governor is positioned in a dedicated air flow path, wherein the dedicated air flow path includes an air inlet open to ambience and an air outlet in fluid communication with the air flow path of the inhaler, and wherein the flow governor is positioned between the air inlet and the air outlet of the dedicated air flow path. 
     36. The medicinal inhaler of embodiment 35, wherein the dedicated air flow path is integrally formed with the housing. 
     37. The medicinal inhaler of embodiment 35, or 36, wherein the dedicated air flow path is formed in a rear portion of the housing, opposite the patient port. 
     38. The medicinal inhaler of embodiment 35 or 36, wherein the dedicated air flow path is formed in a bottom portion of the housing. 
     39. The medicinal inhaler of embodiment 38, wherein the air inlet of the dedicated air flow path is located below the patient port. 
     40. The medicinal inhaler of any of embodiments 30-39, further comprising a cover positioned over the tubular sleeve portion of the housing to seal the open end from ambience, such that any air taken into the inhaler is moved through the flow governor. 
     41. The medicinal inhaler of any of embodiments 30-40, further comprising a skirt seal located between an outer surface of the canister and an inner surface of the housing. 
     42. The medicinal inhaler of any of embodiments 30-41, further comprising a cap configured to be coupled to the tubular sleeve portion of the housing to seal the tubular sleeve portion, the cap defining the air inlet and including the flow governor. 
     43. The medicinal inhaler of any of embodiments 27-42, further comprising a pressure sensor located in the air flow path upstream of the flow governor. 
     44. The medicinal inhaler of any of embodiments 27-43, further comprising a first pressure sensor located in the air flow path upstream of the flow governor and a second pressure sensor located in the air flow path downstream of the flow governor. 
     45. A flow governor assembly for use in a medicinal inhaler, the flow governor assembly comprising: 
     a housing; 
     an air flow path defined by the housing and including an air inlet and an air outlet; and 
     the flow governor of any of embodiments 1-26, the flow governor being positioned in the air flow path between the air inlet and the air outlet. 
     46. The flow governor assembly of embodiment 45, further comprising a first pressure sensor positioned in fluid communication with the air flow path upstream of the flow governor and a second pressure sensor positioned in fluid communication with the air flow path downstream of the flow governor. 
     47. The flow governor assembly of embodiment 45 or 46, further comprising a first pressure sensor located in a first conduit connected to the air flow path upstream of the flow governor and a second pressure sensor located in a second conduit connected to the air flow path downstream of the flow governor. 
     48. The air flow path of embodiment 47, further comprising a constriction located in the air flow path adjacent where the first conduit connects to the air flow path. 
     49. The air flow path of any of embodiments 45-48, further comprising a constriction located between the air inlet and the flow governor. 
     50. A method of using a medicinal inhaler, the method comprising:
         providing a medicinal inhaler comprising a flow governor according to any of embodiments 1-26; and       

     varying an air flow resistance of the inhaler in response to air flow in the air flow path of the flow governor. 
     51. The method of embodiment 50, further comprising inserting a patient port of the medicinal inhaler into a body cavity of a patient; and inhaling through the patient port to cause air flow in the air flow path of the flow governor. 
     52. The method of embodiment 50 or 51, wherein varying the air flow resistance of the inhaler includes flexing the at least one tubular wall inwardly toward the internal support structure. 
     It is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the above description or illustrated in the accompanying drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. It is to be further understood that other embodiments may be utilized, and structural or logical changes may be made without departing from the scope of the present disclosure. 
     The following prophetic examples are intended to be illustrative of the present disclosure and not limiting. 
     EXAMPLES 
     Example 1—Governing Flow Rate 
       FIG. 24  and Table 1 show the calculated range of flowrates that patients will inhale through flow governor assemblies having the configuration of the flow governor assembly  630  of  FIGS. 20 and 21 , comprising the flow governor  101  of  FIGS. 3-8 , with nominal flow governing values of 30, 40 and 50 L/min., respectively. It is clear from  FIG. 24  and Table 1 that the spread in flow rates is greater for the higher flow governor nominal governing flow rates. 
     For modeling purposes, a normal distribution of governing flowrates has been taken around each target governing volumetric flow rate (i.e., 30 L/min., 40 L/min. and 50 L/min.), and the below spreads of data represent the distributions of flow rates at which the flow governors will operate within a population of flow governor assemblies. For example, for the case of a target governing volumetric flow rate of 30 L/min., a small number of flow governors will collapse at around 25 L/min, whereas most would be expected to govern at a flow rate close to the target of 30 L/min, and a small number will govern at a flow rate close to 35 L/min. It is assumed that if a flow governor collapses, then the resistance to flow will increase significantly and the pressure drop will be dominated by the dynamic, or variable, resistance. 
     The below data were calculated by modeling the pressure drop at various flow rates using the following equation:
 
Pressure drop( Pa )=(( R   2   +D   2 )× F   2 )/1000
 
where: R=Static resistance, Pa 0.5 (min./L)
 
     D=Dynamic resistance, Pa 0.5 (min./L) 
     F=Flow rate, L/min 
     The static resistance of the flow governor assembly  630  was estimated to be 0.83 Pa 0.5 (min./L), based on a combination of the resistance from the inlet losses, venturi resistance, the resistance of the flow governor, and the outlet losses. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Ranges of flowrates with governing flow rates of 
               
               
                 30, 40 and 50 L/min. 
               
            
           
           
               
               
               
            
               
                 Nominal governing 
                 Flow rate when 
                 Flow rate when 
               
               
                 flow rate 
                 inhaling at 0.5 kPa 
                 inhaling at 4 kPa 
               
               
                   
               
               
                 30 L/min. 
                 25 L/min. 
                 35 L/min. 
               
               
                 40 L/min. 
                 27 L/min. 
                 45 L/min. 
               
               
                 50 L/min. 
                 27 L/min. 
                 55 L/min. 
               
               
                   
               
            
           
         
       
     
     The inventors have found particular advantages with flow governors of this configuration having a nominal governing flow rate of 30 L/min. 
     Example 2—Air Flow Resistance 
     Another important parameter that can be optimized is the static air flow resistance of the assembly. 
     A flow governor assembly having the configuration of the flow governor assembly  630  of  FIGS. 20-21 , comprising the flow governor  101  of  FIGS. 3-8  was formed having a static resistance of 0.83 Pa 0.5 (min./L) and a nominal governing flow rate of 30 L/min. The performance of such a flow governor assembly is illustrated by the solid trace in  FIG. 25 , derived from data calculated using the equation described above in Example 1. As shown, this design of flow governor assembly will allow a patient who inhales with a pressure drop of only 0.5 kPa to inhale through the assembly at 25 L/min. The other extreme is a patient who creates a pressure drop of 4 kPa, and in this circumstance the inhalation flow rate will be governed according to the tolerance of the flow governor to between approximately 25 and 35 L/min. As is clear from the solid trace, this design ensures that all medications will be delivered within this flow rate range of approximately 25 to 35 L/min., independent of patient lung capacity. This will substantially improve dose consistency for patients (e.g., COPD patients), both inter-patient and intra-patient. All patients will thus benefit from such a flow governor assembly. 
     The dashed trace in  FIG. 25  shows the effect of a higher static resistance for the assembly, of 1.0 Pa 0.5  min./L. Some patients, particularly those who inhale with a pressure drop of only around 0.5 kPa, will not achieve the flow rate required for the flow governor to operate. These patients will not benefit directly from the flow governor. 
     The dotted trace in  FIG. 25  shows the effect of a lower static resistance for the flow governor assembly, of 0.6 Pa 0.5  min./L. All patients will find it easier to inhale through the assembly and some weaker patients will find it easier to obtain a flow rate close to the governing flow rate. However, too low a static resistance can lead to increased drug deposition in the mouth and the throat, which is undesirable, so it is also preferable to avoid the static resistance being too low. 
     
       
         
           
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                 Flow rate when 
                 Flow rate when 
               
               
                 Characteristics 
                 inhaling at 0.5 kPa 
                 inhaling at 4 kPa 
               
               
                   
               
             
            
               
                 30 L/min. flow governor; 
                 28 L/min. 
                 35 L/min. 
               
               
                 0.6 Pa 0.5  min./L static resistance 
               
               
                 30 L/min. flow governor; 
                 25 L/min. 
                 35 L/min. 
               
               
                 0.8 Pa 0.5  min./L static resistance 
               
               
                 30 L/min. flow governor; 
                 22 L/min. 
                 34 L/min. 
               
               
                 1.0 Pa 0.5  min./L static resistance 
               
               
                   
               
            
           
         
       
     
     On the basis of these calculations and these considerations, the ideal static resistance for the flow governor assembly of  FIGS. 20-21  comprising the flow governor of  FIGS. 3-8  with a governing flow rate of 30 L/min. is considered to be around 0.8 Pa 0.5  min./L. At this resistance, practically all COPD and asthma patients would be expected to inhale at a flowrate above about 30 L/min. A higher resistance (e.g. 1.0-1.1 Pa 0.5  min./L) assembly, would result in some COPD patients not being able to reach an inhalation rate of 30 L/min. 
     Typically, only 95% of COPD patients produce an inhalation pressure drop of greater than 0.6 kPa. As a result, provision of flow governor assemblies (and/or inhalers) comprising the flow governors of the present disclosure caters satisfactorily for the vast majority of asthma and COPD patients, who can produce an inhalation pressure drop of between 0.5 and 4.0 kPa. 
     The embodiments described above and illustrated in the figures are presented by way of example only and are not intended as a limitation upon the concepts and principles of the present disclosure. As such, it will be appreciated by one having ordinary skill in the art that various changes in the elements and their configuration and arrangement are possible without departing from the spirit and scope of the present disclosure. 
     All references and publications cited herein are expressly incorporated herein by reference in their entirety into this disclosure. 
     Various features and aspects of the present disclosure are set forth in the following claims.