Patent Publication Number: US-10758157-B2

Title: Determining if airway clearance is required during respiratory therapy

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application claims the priority benefit under 35 U.S.C. § 371 of international patent application no. PCT/IB215/057813, filed Oct. 12, 2015, which claims the priority benefit under 35 U.S.C. § 119(e) of U.S. Provisional Application No. 62/068,279 filed on Oct. 24, 2014, the contents of which are herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present disclosure pertains to a method and apparatus for monitoring the airway of a subject during respiratory therapy to determine if the subject requires airway clearance. 
     2. Description of the Related Art 
     It is well known that secretions can develop in the airway of a subject receiving respiratory therapy. Often when a subject is intubated, the physical presence of foreign material and/or pressure on the oral and lung tissue of the subject may generate secretions in the airway of the subject. In some circumstances, respiratory therapy must be discontinued until the secretions can be cleared from the airway of the subject. 
     SUMMARY OF THE INVENTION 
     Accordingly, one or more aspects of the present disclosure relate to a system configured to detect presence of secretions in an airway of a subject during respiratory therapy and determine whether the subject requires airway clearance. The system includes a pressure generator configured to generate a pressurized flow of breathable gas for delivery to the airway of the subject; one or more sensors configured to generate output signals that convey information related to one or more gas parameters of the pressurized flow of breathable gas delivered to the airway of the subject; one or more physical computer processors operatively connected to the pressure generator and the one or more sensors. The one or more physical computer processors configured by computer readable instructions to: determine a first gas parameter that indicates a volume of breathable gas within the airway of the subject and a second gas parameter that is a time derivative of the first gas parameter; and determine whether to effectuate initiation of airway clearance for the subject based on a perimeter of a plot of the first gas parameter versus the second gas parameter for a complete breathing cycle that includes an inhalation and an exhalation. 
     Yet another aspect of the present disclosure relates to a method configured to detect a presence of secretions in an airway of a subject during respiratory therapy and determine whether the subject requires airway clearance. The method includes generating a pressurized flow of breathable gas for delivery to the airway of the subject; generating output signals that convey information related to one or more gas parameters of the pressurized flow of breathable gas delivered to the airway of the subject; determining a first gas parameter that indicates volume of breathable gas within the airway of the subject and a second gas parameter that is a time derivative of the first gas parameter; and determining whether to effectuate initiation of airway clearance for the subject based on a perimeter of a plot of the first gas parameter versus the second gas parameter for a complete breathing cycle that includes an inhalation and an exhalation. 
     Still another aspect of present disclosure relates to a system configured to detect a presence of secretions in an airway of a subject during respiratory therapy and determine whether the subject requires airway clearance. The system includes means for generating a pressurized flow of breathable gas for delivery to the airway of the subject; means for generating output signals that convey information related to one or more gas parameters of the pressurized flow of breathable gas delivered to the airway of the subject; means for determining a first gas parameter that indicates volume of breathable gas within the airway of the subject and a second gas parameter that is a time derivative of the first gas parameter; and means for determining whether to effectuate initiation of airway clearance for the subject based on a perimeter of a plot of the first gas parameter versus the second gas parameter for a complete breathing cycle that includes an inhalation and an exhalation. 
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration of one embodiment of a secretion detection system configured to determine whether a subject requires airway clearance; 
         FIG. 2  is a plot of flow rate versus volume during at least one inspiration and expiration of a subject; 
         FIG. 3  is a plot of flow rate versus volume during at least one inspiration and expiration of a subject with a noisy signal indicating a need to effectuate initiation of airway clearance for the subject; 
         FIG. 4  is a table illustrating the dimensionless qualities of the perimeter squared normalized by the area of a variety of shapes; and 
         FIG. 5  illustrates a method to determine whether the subject requires airway clearance. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     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  illustrates a system  10  configured to detect presence of secretions in an airway of a subject  12  during respiratory therapy and determine whether the subject requires airway clearance. In some embodiments, system  10  includes one or more of a pressure generator  14 , a subject interface  16 , a sensor  18 , a physical computer processor  20 , a user interface  22 , electronic storage  24 , and/or other components. 
     During respiratory therapy airways may become clogged by tissue secretions which can result in decreased gas delivery to a subject  12 . Clearing the airways is sometimes necessary to continue respiratory therapy. System  10  determines when clearance is required. System  10  plots parameters associated with the respiratory therapy (e.g., a flow rate and a volume of breathable gas) during the inhalations and exhalations of subject  12 . System  10  is configured to analyze a perimeter of the plot and an area of the plot to determine presence of secretions that require airway clearance. In one embodiment, the analysis includes a square of the perimeter of a geometric shape of the plot normalized by the area of the geometric shape of the plot to determine a dimensionless number that can be used to determine when the airway requires clearance. 
     Pressure generator  14  is configured to generate a pressurized flow of gas for delivery to the airway of subject  12 . Pressure generator  14  may control one or more parameters of the flow of gas (e.g., flow rate, pressure, volume, temperature, gas composition, timing, etc.) for therapeutic purposes, and/or for other purposes. By way of a non-limiting example, pressure generator  14  may be configured to control a pressure level of the flow of gas during inhalation and/or exhalation of subject  12  to provide pressure support, inexsufflation therapy, ventilation therapy, and/or other therapies to the airway of subject  12 . 
     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 the airway of subject  12 . In some embodiments, pressure generator  14  receives a flow of gas from a gas source. Pressure generator  14  is any device, such as, for example, a pump, blower, piston, compressor, pressurized wall gas, bellows, and/or other device that is capable of elevating the pressure of the received gas for delivery to subject  12 . Pressure generator  14  may comprise one or more valves for controlling the pressure/flow of gas. The present disclosure also contemplates controlling the operating speed of the blower, either alone or in combination with such valves, to control the pressure/flow of gas provided to the patient. 
     Subject interface  16  is configured to communicate the pressurized flow of breathable gas to the airway of subject  12 . As such, subject interface  16  comprises conduit  40 , interface appliance  42 , and/or other components. Conduit  40  is configured to convey the pressurized flow of gas to interface appliance  42 . Conduit  40  may be and/or include a length of tubing and/or other components configured to convey the pressurized flow of gas to interface appliance  42 . Interface appliance  42  is configured to deliver the flow of gas to the airway of subject  12 . In some embodiments, interface appliance  42  is configured to be non-invasively engaged by the mouth and/or other orifices of subject  12 . Non-invasive engagement comprises removably engaging 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 interface appliance  42 . 
     In some embodiments, interface appliance  42  is removably coupled to conduit  40 . Interface appliance  42  may be removed for cleaning and/or for other purposes. In some embodiments, one end of conduit  40  is configured as a mouthpiece to be engaged by the mouth of subject  12 . 
     In some embodiments, other non-invasive interface appliances may be configured as interface appliance  42 . Some examples of non-invasive interface appliance  42  may comprise, for example, a nasal cannula, a nasal mask, a nasal/oral mask, a full face mask, a total face mask, tracheostomy tube, endotracheal tube, and/or other interface appliances that communicate a flow of gas with an airway of a subject. The present disclosure is not limited to these examples, and contemplates delivery of the flow of gas to the subject using any interface appliance. In some embodiments, system  10  may be connected to a classical respiratory circuit (e.g., a six foot hose) such that the classical respiratory circuit functions as subject interface  16 . 
     Sensor  18  is configured to generate output signals that convey information related to one or more gas parameters of the breathable gas delivered to the airway of subject  12 . Sensor  18  may comprise one or more sensors that generate such information directly. For example, sensor  18  may include pitot tubes configured to detect pressures of breathable gas along subject interface  16  resulting from inhalation and/or exhalations of subject  12 . For example, sensor  18  may detect the pressure, flow, flow rate, volume, and/or other parameters pertaining to the inhalation and/or exhalations of subject  12 . Sensor  18  may comprise one or more sensors that generate output signals conveying information related to inhalations and/or exhalations of subject  12  indirectly. For example, one or more sensors  18  may generate an output based on a heart rate of subject  12  (e.g., sensor  18  may be a heart rate sensor located on the chest of subject  12 , and/or be configured as an optical sensor included in a bracelet on a wrist of subject  12 , and/or be located on another limb of subject  12 ), movement of subject  12  (e.g., sensor  18  may include a bracelet around the wrist and/or ankle of subject  12  with an accelerometer such that sleep may be analyzed using actigraphy signals), changes in skin color of subject  12  (e.g., sensor  18  may include a camera that can detect changes is skin color of subject  12  and infer vital signs such as heart rate, breathing rate, and/or other vital signs from the changes in color), respiration of subject  12 , and/or other characteristics of subject  12 . Although sensor  18  is illustrated at a single location in fluid communication with subject interface  16 , this is not intended to be limiting. Sensor  18  may include sensors disposed in a plurality of locations, such as for example, within (or in communication with) conduit  40 , interface appliance  42 , pressure generator  14 , on subject  12 , and/or in other locations. 
     Processor  20  is configured to provide information processing capabilities in system  10 . As such, processor  20  may comprise 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  20  is shown in  FIG. 1  as a single entity, this is for illustrative purposes only. In some embodiments, processor  20  may comprise a plurality of processing units. These processing units may be physically located within the same device (e.g., subject interface  16 , user interface  22 ), and/or processor  20  may represent processing functionality of a plurality of devices operating in coordination. 
     As shown in  FIG. 1 , processor  20  is configured to execute one or more computer program components. The one or more computer program components may comprise one or more of a parameter component  30 , an analysis component  32 , a secretion determination component  34 , a control component  36 , and/or other components. Processor  20  may be configured to execute components  30 ,  32 ,  34 , and/or  36  by software; hardware; firmware; some combination of software, hardware, and/or firmware; and/or other mechanisms for configuring processing capabilities on processor  20 . 
     It should be appreciated that although components  30 ,  32 ,  34 , and  36  are illustrated in  FIG. 1  as being co-located within a single processing unit, in embodiments in which processor  20  comprises multiple processing units, one or more of components  30 ,  32 ,  34 , and/or  36  may be located remotely from the other components. The description of the functionality provided by the different components  30 ,  32 ,  34 , and/or  36  described below is for illustrative purposes, and is not intended to be limiting, as any of components  30 ,  32 ,  34 , and/or  36  may provide more or less functionality than is described. For example, one or more of components  30 ,  32 ,  34 , and/or  36  may be eliminated, and some or all of its functionality may be provided by other components  30 ,  32 ,  34 , and/or  36 . As another example, processor  20  may be configured to execute one or more additional components that may perform some or all of the functionality attributed below to one of components  30 ,  32 ,  34 , and/or  36 . 
     Parameter component  30  is configured to determine one or more parameters of the pressurized flow of breathable gas. The one or more parameters may comprise gas parameters related to the pressurized flow of breathable gas, breathing parameters related to the respiration of subject  12 , and/or other parameters. Parameter component  30  is configured to determine the one or more parameters based on the output signals of sensors  18 , and/or other information. The information determined by parameter component  30  may be used for controlling pressure generator  14 , stored in electronic storage  24 , generating a plot (described below), and/or used for other uses. 
     The one or more parameters determined by parameter component  30  may include, for example, one or more of a flow rate, a volume, a pressure, humidity, a temperature, an acceleration, a velocity, a timing (e.g., beginning and/or end of inhalation, beginning and/or end of exhalation, etc.), a respiration rate, a duration (e.g., of inhalation, of exhalation, of a single breathing cycle, etc.), respiration frequency, peak flows, peak pressures, and/or other parameters. For example, parameter component  30  may be configured to determine a first gas parameter that indicates a volume of breathable gas within the airway of subject  12  and a second gas parameter that is a time derivative of the first gas parameter (e.g., flow rate). In some embodiments, the parameters may be determined at one or more individual points in time during respiratory therapy. In some embodiments, the parameters may be determined at one or more sampling rates. The one or more sampling rates may be determined at manufacture, determined based on previous respiration of subject  12 , determined based on information entered and/or selected via user interface  22 , determined by one or more of the other components of processor  20 , and/or determined in other ways. 
     Parameter component  30  is configured to plot one or more of the determined parameters on a two-dimensional plot. Individual points on a given plot correspond to values of parameters at individual points in time. In some embodiments, parameter component  30  is configured such that the volume of gas within the airway of subject  12  is plotted through time along one axis of a two dimensional graph. Similarly, parameter component  30  may determine a time derivative of the volume of gas within the airway of subject  12  and plot this parameter for individual points in time (e.g., flow rate) through time on an orthogonal axis of the two dimensional graph. In some embodiments, the time derivative of the volume of gas for individual points in time is and/or or is determined based on the flow rate of gas delivered to subject  12 . In some embodiments, plotted points may be a sampling of values of one or more parameters determined at individual points in time. 
       FIG. 2  illustrates a plot  50  of the volume of gas  52  within the airway of subject  12  versus the flow rate of gas  54  delivered to subject  12 .  FIG. 2  illustrates the inhalation and exhalation of subject  12  in an unobstructed airway.  FIG. 2  shows a normal healthy inspiration and expiration volume for subject  12 . The plot in  FIG. 2  forms a geometric shape (e.g., a generally oval and/or elliptical shape) that has a perimeter  58  and an area  60 . The plot shown in  FIG. 2  lacks significant noise  56  in perimeter  58  and is relatively smooth. In some embodiments, the plot  50  may generate a flow volume loop, a pressure volume loop, a pressure flow loop, and/or other geometric shapes that indicate parameters of inhalation and exhalation of subject  12 . 
     Referring to  FIG. 1  and  FIG. 2 , in some embodiments, analysis component  32  is configured to determine the perimeter  58  and/or the area  60  of plot  50  shown in  FIG. 2 . Analysis component  32  is configured to normalize perimeter  58  by a factor corresponding to the area  60  of plot  50 . In some embodiments, analysis component  32  is configured to normalize perimeter  58  by area  60 . In some embodiments, analysis component  32  is configured to raise perimeter  58  to an exponential power to enhance a noise signal in perimeter  58 . Analysis component  32  enhances the noise signal because the noise signal is indicative of the need for airway clearance in subject  12 . By way of a non-limiting example, analysis component  32  may be configured to determine perimeter  58  of plot  50 , determine area  60  of plot  50 , square perimeter  58 , and normalize perimeter  58  by area  60  to produce a dimensionless metric. In some embodiments, the dimensionless metric produced by the perimeter squared divided by an area is indicative of whether the subject requires airway clearance. For example, a dimensionless metric for a clear breathing cycle (e.g., no secretions present) can be determined and then compared to a dimensionless metric for a current breathing cycle (this comparison is described below). In some embodiments, the dimensionless metric is defined by the parameter Φ as provided by the following equation: 
             Φ   =       P   2     A           
where P is the perimeter  58  and A is the area  60  of the plot  50  generated by parameter component  30 . Dimensionless number Φ has the same value regardless of the size of the geometric shape formed in plot  50 . This makes Φ a value that may be relatively constant for a subject&#39;s individual inspiration and expiration pattern (e.g., when secretions are not present), regardless of the size, lung capacity, and/or other characteristics of subject  12 . Dimensionless number Φ for a current breathing cycle can thus be compared to a secretion free baseline and/or threshold breathing cycle. The comparison of dimensionless metrics for the current breathing cycle and the baseline and/or threshold breathing cycle provides an indication of whether secretions requiring clearance are present, regardless of the characteristics (e.g., size, lung capacity, etc.) of subject  12 .
 
     Returning to  FIG. 1 , secretion determination component  34  is configured to determine whether to effectuate initiation of airway clearance for subject  12 . Secretion determination component  34  is configured to determine whether to effectuate initiation of airway clearance based on the determined perimeter and/or area of a plot (e.g., perimeter  58  and area  60  of plot  50  shown in  FIG. 2 ) of the first gas parameter versus the second gas parameter for a complete breathing cycle that includes an inhalation and an exhalation, based on values of Φ for a current breathing cycle and/or one or more baseline and/or threshold breathing cycles, and/or other information. In some embodiments secretion determination component  34  may compare the dimensionless number Φ determined by analysis component  32  to a threshold value (e.g., baseline value) for Φ to determine if the airway of subject  12  requires clearance. For example, secretion determination component  34  may determine a threshold value for Φ based on previous respiration of subject  12  and compare the threshold value to a current value of Φ determined by analysis component  32  for a current breathing cycle of subject  12 . 
       FIGS. 2 and 3  illustrate how secretion determination component  34  may compare a non-noisy signal  56  (as illustrated in  FIG. 2 ) with a noisy signal  62  (illustrated in  FIG. 3 ) of the same subject  12 . During inhalation, subject  12  without secretions obstructing the airway will generate a relatively smooth inspiratory signal  56  as plotted by parameter component  30  and illustrated in  FIG. 2 . Such a signal may be used by analysis component  32  ( FIG. 1 ) to determine a baseline and/or threshold value for Φ, for example. When an obstruction occludes an airway of subject  12  the signal becomes more ragged generating a noisy inspiratory signal  62 , as illustrated in  FIG. 3 . Analysis component  32  ( FIG. 1 ) determines the perimeter  58 , area  60 , and/or other parameters of the plots shown in  FIG. 2  and/or  FIG. 3  and determines Φ in both cases (e.g., previous respiration shown in  FIG. 2  and a current respiratory cycle as shown in  FIG. 3 ) for comparison. In this way, analysis component  32  can determine in real time the dimensionless quantity Φ which amplifies the noise of the signal (e.g., because the perimeter  58  is squared) and normalizes the signal by the area  60  of normal inspiration and expiration cycles by subject  12  (e.g., the area  60  of the geometric shaped formed by the plot  50  of flow rate versus volume). In this way secretion determination component  34  ( FIG. 1 ) can compare Φ for a current breathing cycle from analysis component  32  to the threshold and/or baseline Φ determined for subject  12  based on previous respiration to determine whether to effectuate initiation of airway clearance for subject  12 . 
     Secretion determination component  34  may be configured to effectuate airway clearance for subject  12  responsive to Φ for a current breathing cycle breaching the threshold and/or baseline value for Φ. Secretion detection component  34  may be configured to effectuate airway clearance responsive to a single breach of the threshold value, one or more breaches of the threshold value, an average value for Φ breaching the threshold value and/or other breaches of the threshold value. Secretion determination component  34  may effectuate airway clearance for subject  12  by controlling pressure generator  14  ( FIG. 1 ) to switch from a pressure support therapy and/or ventilation therapy mode (e.g., controlled by control component  36  described below) to operate in an airway clearance therapy mode. Once airway clearance is complete, secretion determination component  34  may be configured to cause pressure generator  14  to return to the pressure support therapy and/or ventilation therapy mode (e.g., control component  36  may resume control over pressure generator  14 ). 
     Control component  36  is configured to control pressure generator  14  to provide respiratory therapy to subject  12 . Control component  36  is configured to control pressure generator  14  based on the output signals from sensors  18 , parameters determined by parameter component  30 , information entered and/or selected via user interface  22 , and/or other information. In some embodiments, control component  36  is configured such that controlling pressure generator  14  to provide respiratory therapy to subject  12  includes controlling pressure generator  14  to provide the pressurized flow of breathable gas to the airway of subject  12  according to a positive airway pressure support therapy regime (e.g., CPAP, APAP, BiPAP), according to a ventilation therapy regime, and/or according to other respiratory therapy regimes. In some embodiments, control component  36  is configured to control pressure generator  14  to provide a minimum amount of positive airway pressure support during inhalation (e.g., IPAP) and/or exhalation (e.g., EPAP). 
       FIG. 4  illustrates how the dimensionless number Φ retains a constant numeric quantity for a given shape regardless of the size of the shape. For example, a square will have a calculated Φ of 16 regardless of the size of the square. Similarly, a circle will have a determined value of 12.6 for Φ regardless of the radius of the circle. Rectangles can be categorized by the ratio of the height (h) to the base (n*h). This property of Φ is useful because the expected value of a shape enables an estimation of the threshold for secretion determination component  34 . For example, if the shape of subjects  12  plot is a square the threshold value set by secretion determination component  34  could be predetermined (e.g., at manufacture, based on entries and/or selections via user interface  22 , etc.) to be 16. In some embodiments a small deviation from the predicted value may be tolerated (e.g., by setting the threshold value at a number greater than 16). In this example, a care-giver and/or secretion determination component  34  could determine that any value of Φ less than 20 is acceptable, for example. This provides a threshold to compare the real time values of Φ determined by analysis component  32 . 
     Returning to  FIG. 1  user interface  22  is configured to provide an interface between system  10  and subject  12 , and/or other users through which subject  12  and/or other users may provide information to and receive information from system  10 . Other users may comprise, for example, a caregiver, a doctor, and/or other users. This enables data, cues, results, and/or instructions and any other communicable items, collectively referred to as “information,” to be communicated between a user (e.g., subject  12 ) and one or more of pressure generator  14 , processor  20 , and/or other components of system  10 . For example, therapy pressures, the breath rate of subject  12 , a plot of flow rate versus volume, and/or other information may be displayed to a user (e.g., subject  12 ) via user interface  22 . 
     Examples of interface devices suitable for inclusion in user interface  22  comprise a keypad, buttons, switches, a keyboard, knobs, levers, a display screen, a touch screen, speakers, a microphone, an indicator light, an audible alarm, a printer, a tactile feedback device, wireless communications to a secondary device (e.g. a phone, tablet, iPad, and/or secondary devices), and/or other interface devices. In some embodiments, user interface  22  comprises 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  22 . For example, the present disclosure contemplates that user interface  22  may be integrated with a removable storage interface provided by electronic storage  24 . In this example, information may be loaded into system  10  from removable storage (e.g., a smart card, a flash drive, a removable disk, etc.) that enables the user(s) to customize the implementation of system  10 . Other exemplary input devices and techniques adapted for use with system  10  as user interface  22  comprise, 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  22 . 
     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., EEPROM, 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  20 , information received via user interface  22 , 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., user interface  22 , processor  20 , etc.). 
     Control module  58  is configured to control pressure generator  14  to generate the pulse of breathable gas for delivery to the airway of subject  12 . Control module  58  is configured to control pressure generator  14  to deliver the pulse responsive to detection of respiratory sleep events (e.g., airway obstruction) by respiratory event detection module  54 . The pulse is delivered to the airway of subject  12  such that the airway of subject  12  is opened prior to a subsequent inhalation and/or ventilation. Control module  58  is configured to control pressure generator  14  to deliver the pulse in accordance with the pulse parameters obtained and/or adjusted by pulse parameter module  56  prior to the pulse. For example, control module  58  may be configured to control pressure generator  14  to deliver the pulse responsive to detection of airway obstruction and/or in accordance with a timing obtained by pulse parameter module  56 . In some embodiments, the pulse of breathable gas can be a square wave. Moreover, the square wave can have smooth edges to increase comfort and decrease the likelihood of arousing subject  12 . In some embodiments, the pulse of breathable gas can be a saw wave with a ramping time adjusted based on efficacy of the therapy to mitigate obstructions during respiration. Finally, the parameters that will control the duration and magnitude of the pulse of breathable gas may initially be selected from a control menu and then automatically adjusted by control module  58  based on the statistical effectiveness in clearing the airway obstruction of the previous pulses. 
     Control module  58  is configured to control pressure generator  14  to provide the pressurized flow of breathable gas to the airway of the subject according to a positive airway pressure support therapy regime (e.g., CPAP, APAP, BiPAP). Control module  58  is configured to control pressure generator  14  to provide a minimum amount of positive airway pressure support during inhalation (e.g., IPAP) and/or exhalation (e.g., EPAP). Delivering a minimum amount of pressure support and providing a pulse when needed may increase the comfort level of subject  12  during therapy. The minimum amount of positive airway pressure support may comprise delivering the pressurized flow of breathable gas at a minimum pressure level. The minimum pressure level may be configured such that carbon dioxide re-breathing is substantially avoided during pressure support therapy. In some embodiments, the inhalation positive airway pressure may be less than about 7 cmH 2 O. In some embodiments, the inhalation positive airway pressure may be between about 1 cmH 2 O and about 7 cmH 2 O. In some embodiments, the inhalation positive airway pressure level may be zero if there is no carbon dioxide rebreathing by subject  12 . Control module  58  controls pressure generator  14  to deliver the pulse as needed in addition to the positive airway pressure support. 
     Control module  58  is configured to control pressure generator  14  to generate pulses as needed such that subject  12  may maintain a regular breathing pattern.  FIG. 5  illustrates a regular flow rate profile  500  for four consecutive breaths  502 ,  504 ,  506 , and  508 . One or more of breaths  502 ,  504 ,  506 , and/or  508  may be preceded by the control module (shown in  FIG. 1 ) controlling the pressure generator (shown in  FIG. 1 ) to generate a pulse for delivery to the airway of the subject (shown in  FIG. 1 ) such that the subject&#39;s airway is opened prior to and/or at the beginning of the inhalation. 
     Information determined by processor  20  and/or stored by electronic storage  24  may comprise information related to a threshold value of Φ, a current value of Φ, and/or other information. The information stored by electronic storage  24  may be viewed via user interface  22 , by connecting (wired and/or wireless) to a separate computer, and/or other via other methods. The information stored by electronic storage  24  may be used, for example, by a doctor to make medical decisions, and/or for other uses. In some embodiments, system  10  may include a wireless transmitter (not shown) and the information determined by processor  20 , the information stored by electronic storage  24 , and/or other information may be communicated to a care giver, for example, over a wireless network. By way of a non-limiting example, the care giver may receive use information, patient status, and/or other information, allowing the care giver to remotely track the therapy delivered by system  10 . 
       FIG. 5  illustrates a method  500  of delivering a pressurized flow of breathable gas to the airway of a subject and to detect a presence of secretions in an airway of a subject  12  during respiratory therapy to determine whether the subject requires airway clearance. System  10  contains a pressure generator, a subject interface, one or more sensors, and one or more processors. The one or more processors are configured to execute computer program components. The computer program components include a parameter component, an analysis component, a secretion determination component, and/or other components. The operations of method  500  presented below are intended to be illustrative. In some embodiments, method  500  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  500  are illustrated in  FIG. 5  and described below is not intended to be limiting. 
     In some embodiments, method  500  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  500  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  500 . 
     At an operation  502 , a pressurized flow of breathable gas for delivery to the airway of the subject is generated with the pressure generator. In some embodiments, operation  502  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  504 , one or more output signals conveying information related to one or more gas parameters of the pressurized flow of breathable gas delivered to the airway of the subject are generated with the one or more sensors. In some embodiments, operation  504  is performed by sensors the same as or similar to sensors  18  (shown in  FIG. 1  and described herein). 
     At an operation  508 , a first gas parameter that indicates a volume of breathable gas within the airway of the subject and a second gas parameter that is a time derivative of the first gas parameter are determined. In some embodiments, operation  508  is performed by a parameter component is the same as or similar to parameter component  30  (shown in  FIG. 1  and described herein). 
     At an operation  510 , a determination of whether to effectuate initiation of airway clearance for the subject based on a perimeter of a plot of the first gas parameter versus the second gas parameter for a complete breathing cycle that includes an inhalation and an exhalation. Secretions are identified based on the noise level in the output signals and/or the determined parameters. In some embodiments, operation  510  is performed by a secretion determination component  34  the same as or similar to secretion determination component  34  (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.