Patent Publication Number: US-2015075529-A1

Title: System and method for pressure support therapy with shaped airflow

Description:
The present disclosure pertains to an airflow shaping system configured to deliver a shaped, pressurized flow of breathable gas to the airway of a subject. 
     Systems for providing respiratory therapy (e.g., positive airway pressure, inexsufflation, etc.) to subjects are known. These systems generate a pressurized flow of breathable gas that is provided to the airway of a subject to support the subject&#39;s airway. In one type of positive airway pressure (PAP) therapy, known as continuous positive air pressure (CPAP), the pressure of gas delivered to the patient is constant throughout the patient&#39;s breathing cycle. It is also known to provide a positive pressure therapy in which the pressure of gas delivered to the patient varies with the patient&#39;s breathing cycle, or varies with the patient&#39;s effort, to increase the comfort to the patient. During these conventional pressure support therapy techniques the airflow is typically chaotic and/or turbulent. 
     Accordingly, one or more aspects of the present disclosure relate to an airflow shaping system configured to deliver a shaped, pressurized flow of breathable gas to the airway of a subject. The system comprises a pressure generator, a subject interface, and a flow shaper. The pressure generator is configured to generate a flow of breathable gas for delivery to an airway of the subject. The subject interface is configured to place the pressure generator in fluid communication with the airway of the subject. The flow shaper is configured to impart a delivery shape to the flow of breathable gas such that the flow of gas reaches the airway of the subject through the subject interface with the delivery shape imparted by the flow shaper. 
     Yet another aspect of the present disclosure relates to a method of delivering a shaped, pressurized flow of breathable gas to an airway of a subject with an airflow shaping system. The airflow shaping system comprises a pressure generator, a subject interface, and a flow shaper. The method comprises generating the pressurized flow of breathable gas with the pressure generator; communicating the pressurized flow of breathable gas to the airway of the subject with the subject interface; and imparting a delivery shape to the pressurized flow of breathable gas with the flow shaper such that the flow of gas reaches the airway of the subject through the subject interface with the delivery shape imparted by the flow shaper. 
     Still another aspect of the present disclosure relates to an airflow shaping system configured to deliver a shaped, pressurized flow of breathable gas to the airway of a subject. The system comprises means for generating the pressurized flow of breathable gas; means for communicating the pressurized flow of breathable gas to the airway of the subject; and means for imparting a delivery shape to the pressurized flow of breathable gas such that the flow of gas reaches the airway of the subject through the means for communicating with the delivery shape imparted by the means for imparting. 
     These and other objects, features, and characteristics of the present disclosure, as well as the methods of operation and functions of the related elements of structure and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the disclosure. 
    
    
     
         FIG. 1  schematically illustrates an exemplary embodiment of a system configured to deliver a shaped, pressurized flow of breathable gas to the airway of a subject; 
         FIG. 2  shows a flow shaper coupled to a mask; 
         FIG. 3  depicts cyclonic airflow in the airway of a subject; and 
         FIG. 4  illustrates a method of delivering a shaped, pressurized flow of breathable gas to an airway of a subject with an airflow shaping system. 
     
    
    
     As used herein, the singular form of “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise. As used herein, the statement that two or more parts or components are “coupled” shall mean that the parts are joined or operate together either directly or indirectly, i.e., through one or more intermediate parts or components, so long as a link occurs. As used herein, “directly coupled” means that two elements are directly in contact with each other. As used herein, “fixedly coupled” or “fixed” means that two components are coupled so as to move as one while maintaining a constant orientation relative to each other. 
     As used herein, the word “unitary” means a component is created as a single piece or unit. That is, a component that includes pieces that are created separately and then coupled together as a unit is not a “unitary” component or body. As employed herein, the statement that two or more parts or components “engage” one another shall mean that the parts exert a force against one another either directly or through one or more intermediate parts or components. As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality). 
     Directional phrases used herein, such as, for example and without limitation, top, bottom, left, right, upper, lower, front, back, and derivatives thereof, relate to the orientation of the elements shown in the drawings and are not limiting upon the claims unless expressly recited therein. 
       FIG. 1  schematically illustrates an exemplary embodiment of a system  10  configured to deliver a shaped, pressurized flow of breathable gas to the airway of a subject  12 . In some embodiments, system  10  comprises a pressure generator  14 , a subject interface  16 , a flow shaper  18 , one or more sensors  20 , one or more processors  22 , electronic storage  24 , a user interface  26 , and/or other components. 
     Respiratory therapy delivered to a patient&#39;s lungs may be enhanced with a shaped flow of gas. A turbulent flow of gas delivered to a patient&#39;s lungs is inefficient in the amount of energy required to deliver the gas and because it requires more gas energy to reach the lower airways due to resistance from the airway walls. A laminar flow profile is difficult to administer and maintain unless the gas is delivered directly into the airway by invasive means such as a cannula via a transtracheal puncture or endotracheal tube. Gas may be delivered through a convenient non-invasive appliance (e.g., a face mask) with a shaped flow in the form of, for example, toroidal ring vortices, a cyclonic flow, and/or other forms. The result may have several potential benefits including improved gas exchange (recruitment of atelectatic areas, improved oxygenation, minimization of dead space), improved delivery of medications by transporting the aerosolized medication deeper into the lower airways and alveoli regions of the lungs, improvement of the mucociliary transport system, and reduced risk of barotraumas. 
     System  10  may be used for respiratory therapy applications including pressure support therapy, inexsufflation therapy, airway medication delivery, and/or other applications. 
     Pressure generator  14  is configured to provide a pressurized flow of breathable gas for delivery to the airway of subject  12  according to a respiratory therapy regime. The respiratory therapy regime may include one or more of non-invasive ventilation (NIV), CPAP, bi-level positive airway pressure (BPAP), proportional positive airway pressure support (PPAP), inexsufflation therapy, and/or other respiration therapy regimes. Pressure generator  14  receives a flow of gas from a gas source, such as the ambient atmosphere, and elevates the pressure of that gas for delivery to subject  12 . In some embodiments, pressure generator  14  is configured to generate negative pressure to draw gas from subject  12 . Pressure generator  14  may be configured such that one or more gas parameters of the pressurized flow of breathable gas are controlled in accordance with the therapy regime. The one or more gas parameters may include, for example, one or more of pressure, volume, flow rate, temperature, gas composition, velocity, acceleration, and/or other parameters. 
     In some embodiments, pressure generator  14  may include any device, such as, for example, a pump, blower, piston, or bellows, that is capable of elevating the pressure of the received gas for delivery to a patient. In some embodiments, pressure generator  14  may include one or more devices, such as for example, a valve and/or a series of valves, capable of controlling the pressure, flow rate, flow direction, and/or other parameters of the flow of gas. The present disclosure contemplates controlling the operating speed of the blower, for example, either alone or in combination with one or more valves and/or other devices contained in and/or external to pressure generator  14 , to control the pressure and/or flow of gas provided to subject  12 . For example, pressure generator  14  may selectively control the pressure of the flow of gas such that an inspiratory positive airway pressure (IPAP) delivered to the patient is higher than an expiratory positive airway pressure (EPAP) during bi-level pressure support. The present disclosure contemplates that gas other than ambient atmospheric air may be introduced into system  10  for delivery to the patient. 
     Subject interface  16  is configured to interface with the airway of subject  12 . Subject interface  16  is configured to provide fluid communication between pressure generator  14  and the airway of subject  12 . As such, subject interface  16  comprises a conduit  30 , an interface appliance  32 , and/or other components. Conduit  30  is configured to form a flow path through which the pressurized flow of breathable gas is communicated between pressure generator  14  and interface appliance  32 . Conduit  30  may be a flexible length of hose, or other conduit, that places interface appliance  32  in fluid communication with pressure generator  14 . Conduit  30  conveys gas (e.g., air) to and/or from interface appliance  32 , and interface appliance  32  places conduit  30  in communication with the airway of subject  12 . In some embodiments, interface appliance  32  is non-invasive. As such, interface appliance  32  non-invasively engages subject  12 . Non-invasive engagement includes removably engaging an area (or areas) surrounding one or more external orifices of the airway of subject  12  (e.g., nostrils and/or mouth) to communicate gas between the airway of subject  12  and subject interface  16 . Some examples of non-invasive interface appliance  32  may include, for example, a blow tube, a nasal cannula, a nasal mask, a nasal/oral mask, a full face mask, a total face mask, or other interface appliances that communicate a flow of gas with an airway of a subject. 
     Flow shaper  18  is configured to impart a delivery shape to the flow of breathable gas such that the flow of gas reaches the airway of the subject through subject interface  16  with the delivery shape imparted by flow shaper  18 . The delivery shape imparted by flow shaper  18  may refer to geometrical information about a form factor of the flow of gas, timing information (e.g., frequency), scale, rotational information, appearance, physical qualities (e.g., density), and/or other information. In some embodiments, flow shaper  18  may be configured to continuously shape the flow of gas for delivery to subject  12  during a respiratory therapy session. In some embodiments, flow shaper  18  may be configured to shape the flow of gas into a series of one or more air boluses. By way of a non-limiting example, flow shaper  18  may impart a delivery shape to the flow of breathable gas such that the flow of gas reaches the airway of subject  12  configured as a series of ring vortices (toroidal shape). The ring vortices may be formed when the breathable gas passes (e.g., configured as a series of air boluses) through an aperture in flow shaper  18  and pushes up against non-flowing, substantially calm gas in conduit  30 , interface appliance  32 , or another component of system  10 . The flow of gas in the ring vortex may rotate about the circular axis of the ring. By way of another non-limiting example, the shape imparted by flow shaper  18  may comprise cyclonic air flow in which the air flows in a helical pattern. 
     In some embodiments, flow shaper  18  may include components, such as, for example, mechanical components, electromechanical components, a spinning disk, apertures, a diaphragm, vanes, and/or other components capable of shaping the flow of gas for delivery to subject  12 . In some embodiments, the flow of gas from pressure generator  14  may be disrupted by the spinning disk, apertures, vanes, and/or other components to impart a shape to the flow of gas. In some embodiments, flow shaper  18  may be configured with an oscillating membrane that forces gas through an aperture. In some embodiments, flow shaper  18  may include one or more devices, such as for example, a valve and/or a series of valves, capable of controlling the pressure, flow rate, and/or other parameters of the shaped flow of gas. The present disclosure contemplates controlling the shaping components of flow shaper  18  either alone or in combination with the one or more valves and/or other devices contained in and/or external to flow shaper  18 , to control the shape and/or flow of the gas delivered to subject  12  (e.g., air boluses). 
       FIG. 1  shows flow shaper  18  located in subject interface  16  between pressure generator  14  and interface appliance  32 , coupled to conduit  30  on one side and interface appliance  32  on the other. The location of flow shaper  18  in interface appliance  16  is not intended to be limiting. Pressure generator  14  may be directly coupled to flow shaper  18 . Pressure generator  14  may be included in flow shaper  18  such that pressure generation and flow shaping are performed by the same device. Flow shaper  18  may be directly coupled interface appliance  32 . Pressure generator  14 , flow shaper  18 , interface appliance  32 , and/or other components may be coupled such that conduit  30  need not be included in system  10 . In short, any configuration of the components of system  10  that allow system  10  to function as described herein is contemplated by the present disclosure. 
     By way of a non-limiting example,  FIG. 2  shows flow shaper  18  coupled to a mask  200 . The mask is attached to the face of subject  12  with a strap  202 . Flow shaper  18  may receive gas through conduit  30 . Flow shaper  18  may entrain additional air  204  via an entrained air inlet  206 . Entraining additional air may, for example, reduce the amount of source gas (e.g., oxygen) needed to deliver therapeutic levels for effective pulmonary gas exchange. In  FIG. 2 , flow shaper  18  shaped the flow of gas into a series of ring vortices  208 . Flow shaper  18  shaped the ring vortices such that the flow of gas reaches the airway of subject  12  through mask  200  with the ring vortex delivery shape imparted by flow shaper  18 . 
     In some embodiments, flow shaper  18  may be configured to generate and/or shape the pressurized flow of breathable gas for delivery to the airway of subject  12 . As such, flow shaper  18  may receive a flow of gas from a gas source (e.g., the ambient atmosphere, an oxygen cylinder) and elevate the pressure of that gas for delivery to subject  12 . In the example configuration shown in  FIG. 2 , flow shaper  18  may be configured to draw gas in through conduit  30  and/or entrained air inlet  206 . Flow shaper  18  may include any device, such as, for example, a pump, blower, piston, or bellows, that is capable of elevating the pressure of the received gas for delivery to a patient. 
     By way of a second non-limiting example,  FIG. 3  depicts cyclonic airflow  300  in the airway  302  of a subject. Cyclonic airflow is a high speed rotating airflow established within a cylindrical or conical container. Flow shaper  18  (not shown in  FIG. 3 ) may be configured to generate cyclonic airflow by directing the flow of air around the circumference of a cylinder and/or cone within flow shaper  18  such that the air flows in a helical pattern. 
     Returning to  FIG. 1 , sensors  20  are configured to generate output signals conveying information related to one or more gas parameters of the gas within subject interface  16 . The one or more gas parameters may comprise flow rate, pressure, volume, temperature, humidity, velocity, and/or other gas parameters. Sensors  20  may comprise one or more sensors that measure such parameters directly (e.g., through fluid communication with the flow of gas in subject interface  16 ). Sensors  20  may comprise one or more sensors that generate output signals related to one or more parameters of the flow of gas indirectly. By way of a non-limiting example, one or more of sensors  20  may generate an output based on an operating parameter of the pressure generator  14  (e.g., a motor current, voltage, rotational velocity, and/or other operating parameters), and/or other sensors. Although sensors  20  are illustrated at a single location within (or in communication with) conduit  30  between flow shaper  18  and pressure generator  14 , this is not intended to be limiting. Sensors  20  may include sensors disposed in a plurality of locations, such as for example, within pressure generator  14 , within flow shaper  18 , within (or in communication with) interface appliance  32 , and/or other locations. 
     Processor  22  is configured to provide information processing capabilities in system  10 . As such, processor  22  may include one or more of a digital processor, an analog processor, a digital circuit designed to process information, an analog circuit designed to process information, a state machine, and/or other mechanisms for electronically processing information. Although processor  22  is shown in  FIG. 1  as a single entity, this is for illustrative purposes only. In some implementations, processor  22  includes a plurality of processing units. These processing units may be physically located within the same device, or processor  22  may represent processing functionality of a plurality of devices operating in coordination. 
     As shown in  FIG. 1 , processor  22  may be configured to execute one or more computer program modules. The one or more computer program modules comprise one or more of a parameter module  40 , a pressure generator control module  42 , a flow shape control module  44 , and/or other modules. Processor  22  may be configured to execute modules  40 ,  42 , and/or  44  by software; hardware; firmware; some combination of software, hardware, and/or firmware; and/or other mechanisms for configuring processing capabilities on processor  22 . 
     It should be appreciated that although modules  40 ,  42 , and  44  are illustrated in  FIG. 1  as being co-located within a single processing unit, in implementations in which processor  22  includes multiple processing units, one or more of modules  40 ,  42 , and/or  44  may be located remotely from the other modules. The description of the functionality provided by the different modules  40 ,  42 , and/or  44  described below is for illustrative purposes, and is not intended to be limiting, as any of modules  40 ,  42 , and/or  44  may provide more or less functionality than is described. For example, one or more of modules  40 ,  42 , and/or  44  may be eliminated, and some or all of its functionality may be provided by other ones of modules  40 ,  42 , and/or  44 . As another example, processor  22  may be configured to execute one or more additional modules that may perform some or all of the functionality attributed below to one of modules  40 ,  42 , and/or  44 . 
     Parameter module  40  is configured to determine one or more parameters within system  10 . The one or more parameters within system  10  may comprise gas parameters related to the pressurized flow of breathable gas, breathing parameters related to the respiration of subject  12 , shape parameters related to the shape of the flow of gas delivered to subject  12 , and/or other parameters. Parameter module  40  is configured to determine the one or more parameters based on the output signals of sensors  20 , and/or other information. The information determined by parameter module  40  may be used for controlling pressure generator  14 , controlling flow shaper  18 , stored in electronic storage  24 , displayed by user interface  26 , and/or used for other uses. The one or more parameters determined by parameter module  40  may comprise, for example, one or more of a flow rate, flow shape, pressure, a volume, humidity, temperature, acceleration, velocity, respiration rate, tidal volume, and/or other parameters. 
     Pressure generator control module  42  is configured to control pressure generator  14  to generate the flow of gas in accordance with the respiratory therapy regime. The respiratory therapy regime may include one or more of non-invasive ventilation (NIV), CPAP, BPAP, proportional positive airway pressure support (PPAP), inexsufflation therapy, and/or other respiration therapy regimes. Pressure generator control module  42  is configured to control pressure generator  14  based on information related to the output signals from sensors  20 , information determined by parameter module  40 , information entered by a user to user interface  26 , and/or other information. 
     Flow shape control module  44  is configured to control flow shaper  18 . Flow shape control module  44  is configured to control flow shaper  18  to control one or more of the form factor, pressure, volume, frequency, velocity, and/or other parameters of the shape provided by flow shaper  18 . Flow shape control module  44  is configured to control flow shaper  18  based on information related to the output signals from sensors  20 , information determined by parameter module  40 , information entered by a user to user interface  26 , and/or other information. 
     Flow shape control module  44  may be configured to control flow shaper  18  to superimpose the imparted shape on the flow of gas generated by pressure generator  14  (e.g., continuous positive airway pressure support, bi-level pressure support, inexsufflation therapy, etc.). Superimposing the imparted shape on the flow of gas generated by pressure generator  14  may comprise imparting the shape to the flow of gas such that the characteristics (e.g., pressure during inhalation versus pressure during exhalation) of the flow of gas that are related to the therapy regime are still evident. For example, pressure generator  14  may selectively control the pressure of the flow of gas such that an inspiratory positive airway pressure (IPAP) delivered to the patient is higher than an expiratory positive airway pressure (EPAP) during bi-level pressure support. Flow shape control module  44  may control flow shaper  18  to superimpose cyclonic air flow during respiration such that the cyclonic airflow is delivered at the inspiratory pressure and the expiratory pressure generated by pressure generator  14 . 
     In some embodiments, flow shape control module  44  may be configured to control flow shaper  18  to continuously shape the flow of gas for delivery to subject  12  during a therapy session (e.g., bi-level cyclonic airflow described above). In some embodiments, flow shape control module  44  may control flow shaper  18  to shape the flow of gas intermittently (e.g., only during inspiration, during a portion of inspiration, during a portion of inspiration and a portion of expiration, etc.). 
     In some embodiments, flow shape control module  44  may be configured to control flow shaper  18  to shape the flow of gas into a series of one or more air boluses. Flow shape control module  44  may control flow shaper  18  to deliver the boluses of gas continuously and/or intermittently during a therapy session. Flow shape control module  44  may control flow shaper  18  to control the air bolus form factor, volume, pressure, frequency, and/or other parameters. In some embodiments, flow shape control module  44  may control flow shaper  18  such that the air boluses have a pressure of up to about 5 cm H 2 O. In some embodiments, flow shape control module  44  may control flow shaper  18  such that the air boluses have a pressure of up to about 4 cm H 2 O. In some embodiments, flow shape control module  44  may control flow shaper  18  such that the air boluses have a pressure of up to about 3 cm H 2 O. In some embodiments, flow shaper  18  may be configured to deliver air boluses to the airway of subject  12  at a frequency up to  400  boluses per minute. In some embodiments, flow shaper  18  may be configured to deliver the air boluses to the airway of subject  12  at a frequency up to 300 boluses per minute. In some embodiments, flow shaper  18  may be configured to deliver the air boluses to the airway of subject  12  at a frequency up to 200 boluses per minute. 
     In some embodiments, flow shape control module  44  may control flow shaper  18  such that delivery of the air boluses generates a percussive pressure waveform. The percussive pressure waveform may be generated by abruptly alternating the pressure delivered to subject  12  between the bolus pressure and one or more other pressure levels, controlling the frequency of bolus delivery, and/or or by another method. 
     In some embodiments, electronic storage  24  comprises electronic storage media that electronically stores information. The electronic storage media of electronic storage  24  may comprise one or both of system storage that is provided integrally (i.e., substantially non-removable) with system  10  and/or removable storage that is removably connectable to system  10  via, for example, a port (e.g., a USB port, a firewire port, etc.) or a drive (e.g., a disk drive, etc.). Electronic storage  24  may comprise one or more of optically readable storage media (e.g., optical disks, etc.), magnetically readable storage media (e.g., magnetic tape, magnetic hard drive, floppy drive, etc.), electrical charge-based storage media (e.g., EPROM, RAM, etc.), solid-state storage media (e.g., flash drive, etc.), and/or other electronically readable storage media. Electronic storage  24  may store software algorithms, information determined by processor  22 , information received via user interface  26 , and/or other information that enables system  10  to function properly. Electronic storage  24  may be (in whole or in part) a separate component within system  10 , or electronic storage  24  may be provided (in whole or in part) integrally with one or more other components of system  10  (e.g., pressure generator  14 , processor  22 , etc.). In some embodiments, information determined by processor  22  and stored by electronic storage  24  may comprise information related to previous respiration by subject  12 , information related to previous respiration therapy on subject  12  by system  10 , information related to flow shaper  18  and/or other information. 
     User interface  26  is configured to provide an interface between system  10  and subject  12  through which subject  12  provides information to and receives information from system  10 . This enables data, results, and/or instructions and any other communicable items, collectively referred to as “information,” to be communicated between subject  12  and one or more of subject interface  16 , processor  22 , and/or other components of system  10 . Examples of interface devices suitable for inclusion in user interface  26  include a keypad, buttons, switches, a keyboard, knobs, levers, a display screen, a touch screen, speakers, a microphone, a printer, and/or other interface devices. In some embodiments, user interface  26  includes a plurality of separate interfaces. It is to be understood that other communication techniques, either hard-wired or wireless, are also contemplated by the present disclosure as user interface  26 . Other exemplary input devices and techniques adapted for use with system  10  as user interface  26  include, but are not limited to, an RS-232 port, RF link, an IR link, modem (telephone, cable or other). In short, any technique for communicating information with system  10  is contemplated by the present disclosure as user interface  26 . By way of a non-limiting example, a user may set the shape of the flow of gas delivered to subject  12  through user interface  26 . 
     In some embodiments, other information entered by a user through user interface  26  to system  10  may include, for example, designation of a therapy regime (e.g., inexsufflation, CPAP, etc.), flow shape parameters (e.g., frequency, pressure, etc.), and/or other information. 
       FIG. 4  illustrates a method  400  of delivering a shaped, pressurized flow of breathable gas to an airway of a subject with an airflow shaping system. The airflow shaping system comprises a pressure generator, a subject interface, and a flow shaper. The operations of method  400  presented below are intended to be illustrative. In some embodiments, method  400  may be accomplished with one or more additional operations not described, and/or without one or more of the operations discussed. Additionally, the order in which the operations of method  400  are illustrated in  FIG. 4  and described below is not intended to be limiting. 
     In some embodiments, method  400  may be implemented in one or more processing devices (e.g., a digital processor, an analog processor, a digital circuit designed to process information, an analog circuit designed to process information, a state machine, and/or other mechanisms for electronically processing information). The one or more processing devices may include one or more devices executing some or all of the operations of method  400  in response to instructions stored electronically on an electronic storage medium. The one or more processing devices may include one or more devices configured through hardware, firmware, and/or software to be specifically designed for execution of one or more of the operations of method  400 . 
     At an operation  402 , a pressurized flow of breathable gas is generated for delivery to an airway of a subject. In some embodiments, operation  402  is performed by a pressure generator the same as or similar to pressure generator  14  (shown in  FIG. 1  and described herein). 
     At an operation  404 , the pressurized flow of breathable gas is communicated to the airway of the subject with a subject interface. In some embodiments, operation  404  is performed by a subject interface the same as or similar to subject interface  16  (shown in  FIG. 1  and described herein). 
     At an operation  406 , a delivery shape is imparted to the flow of breathable gas. The delivery shape is imparted to the flow of breathable gas such that the flow of gas reaches the airway of the subject with the imparted delivery shape. In some embodiments, operation  406  is performed by a flow shaper the same as or similar to flow shaper  18  (shown in  FIG. 1  and described herein). 
     In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word “comprising” or “including” does not exclude the presence of elements or steps other than those listed in a claim. In a device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. In any device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain elements are recited in mutually different dependent claims does not indicate that these elements cannot be used in combination. 
     Although the description provided above provides detail for the purpose of illustration based on what is currently considered to be the most practical and preferred embodiments, it is to be understood that such detail is solely for that purpose and that the disclosure is not limited to the expressly disclosed embodiments, but, on the contrary, is intended to cover modifications and equivalent arrangements that are within the spirit and scope of the appended claims. For example, it is to be understood that the present disclosure contemplates that, to the extent possible, one or more features of any embodiment can be combined with one or more features of any other embodiment.