Patent Publication Number: US-2019192795-A1

Title: Expiratory flow limitation detection via flow resistor adjustment

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application claims the priority benefit under 35 U.S.C. § 119(e) of U.S. Provisional Application No. 62/610,736, filed on Dec. 27, 2017, the contents of which are herein incorporated by reference. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     The present disclosure pertains to a method and a system for detecting an Expiratory Flow Limitation (EFL) of a patient. 
     2. Description of the Related Art 
     Chronic Obstructive Pulmonary Disease (COPD) is a public health problem. It is the fourth leading cause of chronic morbidity and mortality in the United States, affecting over 24 million Americans. It is the third leading cause of death in the United States after heart disease and cancer and, by 2020, it is projected to be the third leading cause of death worldwide. The increased mortality is driven by the expanding epidemic of smoking and the aging population worldwide. 
     COPD is an umbrella term used to describe progressive lung diseases including emphysema, chronic bronchitis, non-reversible asthma, and some forms of bronchiectasis. COPD is characterized by increasing breathlessness. Patients with COPD may have difficulty exhaling because of the deterioration of their lung tissue or the inflammation of their airway walls. This condition is commonly referred to as Expiratory Flow Limitation (EFL) and it affects the quality of life and can ultimately contribute to acute respiratory failure. As an example, the expiratory flow limitation relates to a physiological condition where a person&#39;s airways partially collapse due to a loss of their elastic recoil due to parenchymal destruction or to some other form of airway obstruction. “The definition of EFL implies that a further increase in transpulmonary pressure will cause no further increase in expiratory flow,” as disclosed in N. G. Koulouris et al., “Methods for assessing expiratory flow limitation during tidal breathing in COPD patients,” Pulmonary Medicine, vol. 2012, doi:10.1155/2012/234145. The expiratory flow limitation of a subject is determined by detecting via one or more sensors when flow ceases to increase despite increasing expiratory effort. A patient with EFL cannot increase his flow rate by force and often increases his dynamic volume towards Total Lung Capacity, TLC (dynamic hyperinflation) causing muscle fatigue. Also, a patient with EFL has a lower exercise tolerance and chronic dyspnea, leading to an unhealthy, sedentary life-style. 
     Common treatments for EFL are the application of positive airway pressure and/or pharmaceuticals. 
     With patients in the ICU, EFL is detected with a manual maneuver. A clinician/respiratory therapist exerts force on the patient&#39;s abdomen at the onset of exhalation. That is, the physician may simply press on the ventilated patient during expiration and determine if there is or there is not an increase in flow. This force causes an increase in the pressure difference between the lungs and mouth that should drive the exhalation flow. If the patient has EFL, the exhalation flow does not increase. This manual chest compression technique i) does not require patient collaboration, ii) lacks repeatability (manual operation), and iii) needs skilled personnel. The manual chest compression technique is also not applicable for a chronic patient at home. 
     Other techniques for the detection of EFL are the ΔXrs with forced oscillation technique (FOT) and the negative expiratory pressure (NEP) method. 
     For example, the NEP method i) does not require patient collaboration, ii) requires negative pressure (or at least positive pressure), and iii) can result in upper airway artifacts. The FOT method i) does not require patient collaboration and ii) requires generation of pressure oscillations. 
     Further, the FOT and NEP method are available as stand-alone devices or as part of multifunctional spirometers. The FOT and NEP method are typically used for non-ventilated patients. The NEP method is conceptually similar to the application of pressure on the abdomen. It replaces the increasing pressure in the lungs from abdominal compression with negative pressure applied at the mouth. The ΔXrs with the FOT method relies on the change in the reactance of the respiratory system when EFL occurs. In order to “measure” the reactance, a forced sinusoidal pressure signal is applied. In primary care settings, the ratio between FEV1 (forced expiratory volume in 1 second) and FVC (functional vital capacity) obtained from spirometry is typically used. 
     Therefore, an improved system and method for detecting an Expiratory Flow Limitation (EFL) of a patient is needed. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of one or more embodiments of the present patent application to provide a system for detecting an Expiratory Flow Limitation (EFL) of a patient. The system comprises an inhalation passage that brings inhaled air to the patient; an exhalation passage that takes exhaled air away from the patient; a sensor for measuring flow-volume information of the exhaled air through the exhalation passage; a flow resistor positioned in the exhalation passage and being adjustable to provide an exhalation resistance in the exhalation passage; and a computer system that comprises one or more physical processors operatively connected with the sensor and the flow resistor. In one embodiment, the one or more physical processors are programmed with computer program instructions which, when executed cause the computer system to: determine a reference expiratory flow-volume curve using flow-volume information of the exhaled air through the exhalation passage when a reference exhalation resistance is provided by the flow resistor in the exhalation passage; adjust the flow resistor to lower the exhalation resistance below the reference exhalation resistance; determine a perturbed expiratory flow-volume curve using flow-volume information of the exhaled air through the exhalation passage when the lowered exhalation resistance is provided by the flow resistor in the exhalation passage; and detect the EFL of the patient based on (i) the determined perturbed expiratory flow-volume curve and (ii) the determined reference expiratory flow-volume curve. 
     It is yet another aspect of one or more embodiments of the present patent application to provide a method for detecting an Expiratory Flow Limitation (EFL) of a patient. The method is implemented by a computer system that comprises one or more physical processors executing computer program instructions which, when executed, perform the method. The method comprises obtaining, from one or more sensors, flow-volume information of exhaled air through an exhalation passage; determining, by the computer system, a reference expiratory flow-volume curve using flow-volume information of the exhaled air through the exhalation passage when a reference exhalation resistance is provided by a flow resistor in the exhalation passage; adjusting the flow resistor to lower the exhalation resistance below the reference exhalation resistance; determining, by the computer system, a perturbed expiratory flow-volume curve using flow-volume information of the exhaled air through the exhalation passage when the lowered exhalation resistance is provided by the flow resistor in the exhalation passage; and detecting, by the computer system, the Expiratory Flow Limitation (EFL) of the patient based on (i) the determined perturbed expiratory flow-volume curve (ii) the determined reference expiratory flow-volume curve. 
     It is yet another aspect of one or more embodiments to provide a system for detecting an Expiratory Flow Limitation (EFL) of a patient. The system comprises a means for executing machine-readable instructions with at least one physical processor. The machine-readable instructions comprises obtaining, from one or more sensors, flow-volume information of exhaled air through an exhalation passage; determining a reference expiratory flow-volume curve using flow-volume information of the exhaled air through the exhalation passage when a reference exhalation resistance is provided by a flow resistor in the exhalation passage; adjusting the flow resistor to lower the exhalation resistance below the reference exhalation resistance; determining a perturbed expiratory flow-volume curve using flow-volume information of the exhaled air through the exhalation passage when the lowered exhalation resistance is provided by the flow resistor in the exhalation passage; and detecting the Expiratory Flow Limitation (EFL) of the patient based on (i) the determined perturbed expiratory flow-volume curve (ii) the determined reference expiratory flow-volume curve. 
     These and other objects, features, and characteristics of the present patent application, 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 present patent application. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exemplary system for detecting an Expiratory Flow Limitation (EFL) of a patient in accordance with an embodiment of the present patent application; 
         FIG. 2  is an exemplary system for detecting EFL of the patient in accordance with another embodiment of the present patent application; 
         FIG. 3  is an exemplary system for detecting EFL of the patient in accordance with another embodiment of the present patent application; 
         FIG. 4  is an exemplary system for detecting EFL of the patient in accordance with another embodiment of the present patent application; 
         FIG. 5  shows a graphical illustration of an exemplary exhalation resistance reduction on select breaths in the system for detecting the EFL of the patient in accordance with an embodiment of the present patent application; 
         FIG. 6  shows exemplary flow comparisons between perturbed breath flow-volume curves and reference breaths flow-volume curves obtained from the system for detecting the EFL of the patient in accordance with an embodiment of the present patent application; 
         FIG. 7  shows exemplary EFL detection by reduction of exhalation resistance in the system for detecting the EFL of the patient and corresponding treatment to abolish EFL using the same system in accordance with an embodiment of the present patent application; and 
         FIG. 8  shows an exemplary method for detecting EFL of the patient and corresponding abolishment of the EFL in accordance with an embodiment of the present patent application. 
     
    
    
     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 term “or” means “and/or” unless the context clearly dictates otherwise. 
     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. 
     The present patent application provides a system  100  for detecting an Expiratory Flow Limitation (EFL) of a patient. System  100  comprises an inhalation passage  104  that brings inhaled air to the patient; an exhalation passage  108  that takes exhaled air away from the patient; a sensor  106  for measuring flow-volume information of the exhaled air through exhalation passage  108 ; a flow resistor  110  positioned in exhalation passage  108  and being adjustable to provide an exhalation resistance in exhalation passage  108 ; and a computer system  102  that comprises one or more physical processors operatively connected with sensor  106  and flow resistor  110 . 
     In one embodiment, the one or more physical processors of computer system  102  are programmed with computer program instructions which, when executed cause computer system  102  to: determine a reference expiratory flow-volume curve using flow-volume information of the exhaled air through exhalation passage  108  when a reference exhalation resistance is provided by flow resistor  110  in exhalation passage  108 ; adjust flow resistor  110  to lower the exhalation resistance below the reference exhalation resistance; determine a perturbed expiratory flow-volume curve using flow-volume information of the exhaled air through exhalation passage  108  when the lowered exhalation resistance is provided by flow resistor  110  in the exhalation passage; and detect the Expiratory Flow Limitation (EFL) of the patient based on i) the determined perturbed expiratory flow-volume curve and ii) the determined reference expiratory flow-volume curve. 
     In one embodiment, system  100  is configured for facilitating expiratory flow limitation detection via automated adjustment of flow resistor  110  placed in exhalation passage  108 . In one embodiment, a hand-held, low-cost, state-of-the-art lung function measurement instrument/system  100  that has been exclusively designed to detect the presence of EFL in COPD patients is disclosed in the present patent application. In one embodiment, system  100  includes a pneumatic circuit and device/system  100  as shown in  FIG. 1 . In one embodiment, system  100  includes a pneumatic circuit as shown in  FIG. 3 . In one embodiment, system  100  includes a pneumatic circuit as shown in  FIG. 4 . In one embodiment, system  100  may be a system as shown in  FIG. 2 . In one embodiment, system  100  includes an adjustable Positive Expiratory Pressure (PEP) therapy or PEP spirometer system/device. 
     In one embodiment, referring to  FIGS. 1-4 , system  100  includes tubing or conduit portions that form inhalation passage  104 . In one embodiment, inhalation passage  104  is configured to bring inhaled air to the patient. 
     In one embodiment, system  100  includes an inhalation valve  107  that is configured to be in communication with inhalation passage  104 . In one embodiment, inhalation valve  107  includes a check valve. In one embodiment, inhalation valve  107  includes a ball valve. In one embodiment, inhalation valve  107  includes a one-way valve. In one embodiment, inhalation valve  107  includes a controllable valve. In one embodiment, inhalation valve  107  may be any valve assembly that is configured to bring inhaled air to the patient (i.e., to allow a patient to breath in). In one embodiment, the direction of flow of gas/air in inhalation passage  104  is opposite to that in exhalation passage  108  as shown by the arrows in  FIGS. 1, 3, and 4 . 
     In one embodiment, each respiration cycle generally includes an inhalation phase and an exhalation phase. In one embodiment, during the inhalation phase, inhalation valve  107  is open and exhalation valve  109  is closed. That is, during the inhalation phase, a flow of gas (e.g., at ambient pressure P amb ) passes through the open inhalation valve  107 , through inhalation passage  104  into the patient&#39;s mouth (airways and lungs). In one embodiment, air at ambient pressure P amb  is drawn into the inhalation passage  104 , for example, through inhalation valve  107 . That is, inhalation valve  107  is configured to open to allow the patient to inhale substantially resistance free. In one embodiment, the flow of gas is drawn through an inlet opening  103  of system  100 . During the exhalation phase, air is prevented from exiting through the inlet opening  103  by the closing of the inhalation valve  107 . 
     In one embodiment, during the inhalation phase, the pressure at the mouth of the patient is approximately equal to the ambient pressure, P amb  (i.e., 0 cm H 2 0), whereas, during the exhalation phase, air goes through resistive element or resistor  110  that causes a drop in pressure, i.e., the pressure at the mouth P mouth  will be higher than the ambient pressure, P amb  (as illustrated in  FIG. 5 ). 
     In one embodiment, system  100  is also configured to detect the start and end of the exhalation phase. In one embodiment, system  100  includes an algorithm to detect the start and end of the exhalation phase. 
     In one embodiment, system  100  includes tubing or conduit portions that form exhalation passage  108 . In one embodiment, exhalation passage  108  is configured to take the exhaled air away from the patient. In one embodiment, as shown in  FIG. 4 , exhalation passage  108  of system  100  includes a check valve  119 . In one embodiment, as shown in  FIG. 4 , exhalation passage  108  includes an on-off valve  109 . In one embodiment, as shown in  FIG. 4 , exhalation passage  108  includes both check valve  119  and on-off valve  109 . In one embodiment, exhalation valve  109 / 119  are configured to be in communication with exhalation passage  108 . In one embodiment, exhalation valve  109 / 119  may be any valve assembly that is configured to control/allow the flow of the exhaled air from the patient to escape to atmosphere through exhalation passage  108 . In one embodiment, exhalation valve  109  includes a solenoid or electromechanical operated valve. In one embodiment, exhalation valve  119  includes a ball valve. In one embodiment, exhalation valve  119  includes a check valve. In one embodiment, exhalation valve  119  includes a one-way valve. 
     In one embodiment, system  100  is configured to control a variable resistance during the patient&#39;s exhalation. In one embodiment, system  100  is also configured to remove a variable resistance during the patient&#39;s exhalation as will be described in detail below. 
     In one embodiment, system  100  includes flow resistor  110  that is positioned in exhalation passage  108 . In one embodiment, flow resistor  110  may include a flow resistive element. In one embodiment, flow resistor  110  may be an electro-flow resistive element. In one embodiment, flow resistor  110  may be a mechanical flow resistive element. In one embodiment, flow resistor  110  may be an electro-mechanical flow resistive element. In one embodiment, flow resistor  110  may be any flow resistive element that is configured to provide an exhalation resistance in exhalation passage  108 . 
     In one embodiment, flow resistor  110  is configured to be adjustable to provide an exhalation resistance in exhalation passage  108 . In one embodiment, the exhalation resistance provided by flow resistor  110  is configured to be decreased on select breaths in order to increase the exhalation pressure drive and mimic the abdomen compression maneuver as will be described in detail below. 
     In one embodiment, flow resistor  110  is configured to be manually actuated and/or adjustable. In one embodiment, flow resistor  110  is configured to be mechanically actuated and/or adjustable. 
     In one embodiment, flow resistor  110  is configured to be operatively connected with one or more physical processors of computer system  102 . In one embodiment, as will be described in detail below, flow resistor  110  is configured to be adjustable by computer system  102 . In one embodiment, as will be described in detail below with respect to system  100  in  FIG. 2 , flow resistor  110  is configured to be adjustable by a flow resistor subsystem  114  of computer system  102 . 
     In one embodiment, system  100  includes sensor  106  to measure the flow of the gas/air exhaled by the patient. In one embodiment, sensor  106  is configured to measure and provide respiratory parameters such as flow rate, flow-volume, etc. In one embodiment, sensor  106  is configured to measure flow-volume information of the exhaled air through exhalation passage  108 . In one embodiment, sensor  106  is configured to measure volumetric flow rate of the exhaled air through exhalation passage  108 . 
     In one embodiment, sensor  106  is a flow sensor. In one embodiment, sensor  106  is a pressure sensor. In one embodiment, sensor  106  includes a flow sensor and a pressure sensor. 
     In one embodiment, sensor  106  is in fluid communication with exhalation passage  108 . During the exhalation/expiration phase, sensor  106  is configured to measure the flow through and/or pressure in exhalation passage  108 . In one embodiment, sensor  106  may be calibrated to sense the beginning of exhalation/expiration phase and to begin the sensing procedure. In one embodiment, sensor  106  is configured to be operatively connected with one or more physical processors of computer system  102 . In one embodiment, sensor  106  is configured to be operatively connected with reference expiratory flow-volume curve determination subsystem  112  and perturbed expiratory flow-volume curve determination subsystem  116  of computer system  102 . In one embodiment, sensor  106  is configured to be operatively connected with a database (e.g., database  132 ) to save the flow-volume information of the exhaled air through exhalation passage  108  into the database. Saved flow-volume information of the exhaled air through exhalation passage  108  may later retrieved from the database as needed. 
     In one embodiment, system  100  includes a mouthpiece  111  through which the patient breathes into system  100 . In one embodiment, mouthpiece  111  may be of the type where the patient takes the part of mouthpiece  111  into his/her mouth. In one embodiment, system  100  includes a mask  111  through which the patent breathes into system  100 . In one embodiment, mask or mouthpiece  111  is configured to be removably connected to system  100 . In one embodiment, the patient discharges expiratory air into mask or mouthpiece  111 . 
       FIG. 2  shows system  100  for detecting EFL of a patient, in accordance with one or more embodiments. As shown in  FIG. 2 , system  100  may comprise server  102  (or multiple servers  102 ). Server  102  may comprise reference expiratory flow-volume curve determination subsystem  112 , flow resistor adjustment subsystem  114 , perturbed expiratory flow-volume curve determination subsystem  116 , Expiratory Flow Limitation (EFL) detection subsystem  118 , Expiratory Flow Limitation abolishment subsystem  120 , or other components or subsystems. 
     In one embodiment, Expiratory Flow Limitation abolishment subsystem  120  is optional. It should be appreciated that the description of the functionality provided by the different subsystems  112 - 120  described herein is for illustrative purposes, and is not intended to be limiting, as any of subsystems  112 - 120  may provide more or less functionality than is described. For example, one or more of subsystems  112 - 120  may be eliminated, and some or all of its functionality may be provided by other ones of subsystems  112 - 120 . As another example, additional subsystems may be programmed to perform some or all of the functionality attributed herein to one of subsystems  112 - 120 . 
     In one embodiment, reference expiratory flow-volume curve determination subsystem  112  is configured to determine a reference expiratory flow-volume curve using flow-volume information of the exhaled air through exhalation passage  108  when a reference exhalation resistance is provided by flow resistor  110  in exhalation passage  108 . 
     In one embodiment, the set or reference exhalation resistance may be obtained by clinical testing. In one embodiment, the set or reference exhalation resistance may be obtained using data analytics. In one embodiment, the set or reference exhalation resistance may be obtained from research publications. In one embodiment, the reference or set expiratory resistance may be saved into a database (e.g., database  132 ) and retrieved from the database as needed. In one embodiment, subsystem of system  100  may continuously update/modify the reference or set expiratory resistance. In one embodiment, the set or reference exhalation resistance is configured such that the resulting positive expiratory pressure is constant or approximately so. 
     In one embodiment, reference expiratory flow-volume curve determination subsystem  112  may obtain information associated with exhalation passage  108  when a reference exhalation resistance is provided by flow resistor  110  in exhalation passage  108 . In one embodiment, the information may include flow-volume information, flow information, pressure information, or any other related information. In one embodiment, the flow-volume information of the patient may include information about flow-volume in exhalation passage  108  when a reference exhalation resistance is provided by flow resistor  110  in exhalation passage  108 . In one embodiment, the flow information of the patient may include information about flow through exhalation passage  108  when a reference exhalation resistance is provided by flow resistor  110  in exhalation passage  108 . In one embodiment, the pressure information of the patient may include information about pressure in exhalation passage  108  when a reference exhalation resistance is provided by flow resistor  110  in exhalation passage  108 . 
     As another example, the information may be obtained from one or more monitoring devices (e.g., flow monitoring device, pressure monitoring device, or other monitoring devices). In one embodiment, one or more monitoring devices and associated sensors  106  may be configured to monitor flow-volume in exhalation passage  108  when a reference exhalation resistance is provided by flow resistor  110  in exhalation passage  108 . In one embodiment, one or more monitoring devices and associated sensors  106  may be configured to monitor flow through exhalation passage  108  when a reference exhalation resistance is provided by flow resistor  110  in exhalation passage  108 . In one embodiment, one or more monitoring devices and associated sensors  106  may be configured to monitor pressure in exhalation passage  108  when a reference exhalation resistance is provided by flow resistor  110  in exhalation passage  108 . These monitoring devices may include one or more sensors  106 , such as pressure sensors, pressure transducers, flow rate sensors, flow sensors, volume sensors, or other sensors. Sensors may, for instance, be configured to obtain information of the patient (e.g., pressure, flow, flow-volume, volume, or any other related parameters) or other information related to exhalation passage  108  when a reference exhalation resistance is provided by flow resistor  110  in exhalation passage  108 . 
     In one scenario, a monitoring device may obtain information (e.g., based on information from one or more sensors  106 ), and provide information to a computer system (e.g., comprising server  102 ) over a network (e.g., network  150 ) for processing. In another scenario, upon obtaining the information, the monitoring device may process the obtained information, and provide processed information to the computer system over a network (e.g., network  150 ). In yet another scenario, the monitoring device may automatically provide information (e.g., obtained or processed) to the computer system (e.g., comprising server  102 ). 
     In one embodiment, reference expiratory flow-volume curve determination subsystem  112  is configured to determine the reference expiratory flow-volume curve from the obtained flow-volume information when a reference exhalation resistance is provided by flow resistor  110  in exhalation passage  108 . That is, reference expiratory flow-volume curve determination subsystem  112  is configured to analyze information/data from a device&#39;s flow and pressure sensors and calculate or determine reference expiratory flow-volume curve based on the sensor data/information. In one embodiment, reference expiratory flow-volume curve determination subsystem  112  may be configured to determine the reference expiratory flow-volume curve directly from the flow and pressure signals. 
     In one embodiment, flow resistor adjustment subsystem  114  is configured to be operatively associated with flow resistor  110 . In one embodiment, flow resistor adjustment subsystem  114  is configured to control a variable resistance during the patient&#39;s exhalation. In one embodiment, flow resistor adjustment subsystem  114  is also configured to remove a variable resistance during the patient&#39;s exhalation. 
     In one embodiment, flow resistor adjustment subsystem  114  is configured to adjust flow resistor  110  to the reference exhalation resistance. In one embodiment, flow resistor adjustment subsystem  114  is configured to adjust flow resistor  110  to lower the exhalation resistance below the reference exhalation resistance. In one embodiment, flow resistor adjustment subsystem  114  is configured to decrease (or reduce/drop) the exhalation resistance on select breaths. In one embodiment, flow resistor adjustment subsystem  114  is configured to adjust/change the exhalation resistance, for example, to abolish EFL. In one embodiment, flow resistor adjustment subsystem  114  is configured to increase the reference exhalation resistance on a select breath. 
     In one embodiment, the configuration, operation and structure of perturbed expiratory flow-volume curve determination subsystem  116  are similar that of reference expiratory flow-volume curve determination subsystem  112  except for the differences noted below. In one embodiment, perturbed expiratory flow-volume curve determination subsystem  116  is configured to determine a perturbed expiratory flow-volume curve using flow-volume information of the exhaled air through exhalation passage  108  when the lowered exhalation resistance (i.e., below the set/reference exhalation resistance) is provided by flow resistor  110  in exhalation passage  108 . 
     In one embodiment, perturbed expiratory flow-volume curve determination subsystem  116  may obtain information associated with exhalation passage  108  when the lowered exhalation resistance (i.e., below the set/reference exhalation resistance) is provided by flow resistor  110  in exhalation passage  108 . In one embodiment, the information may include flow-volume information, flow information, pressure information, or any other related information when a lowered exhalation resistance (i.e., below the set/reference exhalation resistance) is provided by flow resistor  110  in exhalation passage  108 . In one embodiment, one or more monitoring devices and associated sensors  106  may be configured to monitor flow-volume, flow, pressure, or other related information in exhalation passage  108  when a lowered exhalation resistance (i.e., below the set/reference exhalation resistance) is provided by flow resistor  110  in exhalation passage  108 . 
     In one embodiment, perturbed expiratory flow-volume curve determination subsystem  116  is configured to determine the perturbed expiratory flow-volume curve from the obtained flow-volume information when a lowered exhalation resistance (i.e., below the set/reference exhalation resistance) is provided by flow resistor  110  in exhalation passage  108 . That is, perturbed expiratory flow-volume curve determination subsystem  116  is configured to analyze information/data from a device&#39;s flow and pressure sensors and calculate or determine perturbed expiratory flow-volume curve based on the sensor data/information. In one embodiment, perturbed expiratory flow-volume curve determination subsystem  116  may be configured to determine the perturbed expiratory flow-volume curve directly from the flow and pressure signals. 
     In one embodiment, system  100  includes an algorithm to compute exhalation flow-volume curves. In one embodiment, reference expiratory flow-volume curve determination subsystem  112  and perturbed expiratory flow-volume curve determination subsystem  116  of system  100  each includes an algorithm to compute the exhalation flow-volume curves. That is, in one embodiment, reference expiratory flow-volume curve determination subsystem  112  is configured to determine, using an algorithm, a reference expiratory flow-volume curve using flow-volume information of the exhaled air through exhalation passage  108  when a reference exhalation resistance is provided by flow resistor  110  in exhalation passage  108 . In one embodiment, perturbed expiratory flow-volume curve determination subsystem  116  is configured to determine, using an algorithm, a perturbed expiratory flow-volume curve using flow-volume information of the exhaled air through exhalation passage  108  when the lowered exhalation resistance (i.e., below the set/reference exhalation resistance) is provided by flow resistor  110  in exhalation passage  108 . 
     In one embodiment, Expiratory Flow Limitation (EFL) detection subsystem  118  is configured to detect the Expiratory Flow Limitation (EFL) of the patient based on i) the determined perturbed expiratory flow-volume curve (e.g., from reference expiratory flow-volume curve determination subsystem  112 ) and ii) the determined reference expiratory flow-volume curve (e.g., from perturbed expiratory flow-volume curve determination subsystem  116 ). In one embodiment, Expiratory Flow Limitation (EFL) detection subsystem  118  is configured to detect the Expiratory Flow Limitation (EFL) of the patient by comparing the determined perturbed expiratory flow-volume curve (e.g., from reference expiratory flow-volume curve determination subsystem  112 ) with the determined reference expiratory flow-volume curve (e.g., from perturbed expiratory flow-volume curve determination subsystem  116 ). 
     In one embodiment, the presence of EFL is assessed by comparing the flow-volume curves of two breaths (i.e., a reference breath and a perturbed breath with exhalation resistance lower than the reference breath). 
     In one embodiment, the reference expiratory flow-volume curve and the perturbed expiratory flow-volume curve are displayed to the caregiver for a visual assessment of the breath. In one embodiment, the classification (i.e., EFL vs. no EFL) is done by the caregiver. 
     In one embodiment, system  100  also includes a user interface and/or other components. In one embodiment, the user interface is configured to provide an interface between system  100  and the patient/caregiver/physician. In one embodiment, the reference expiratory flow-volume curve and the perturbed expiratory flow-volume curve are displayed to the caregiver/physician via the user interface. In one embodiment, the caregiver/physician may specify one or more PEP therapy regimes that are to be delivered to the patient using the user interface. Examples of interface devices suitable for inclusion in the user interface 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, and/or other interface devices. In one embodiment, the user interface comprises a plurality of separate interfaces. In one embodiment, the user interface comprises at least one interface that is provided integrally with system  100 . 
     In one embodiment, the classification (i.e., EFL vs. no EFL) is automated. In one embodiment, the classification (i.e., EFL vs. no EFL) is done by an algorithm run by one or more processors of computer system  102  within system  100 . In one embodiment, the classification (i.e., EFL vs. no EFL) is done by an algorithm run by one or more processors of computer system  102  outside system  100 . That is, system  100  includes an automatic algorithm to determine test result (i.e., EFL vs. no EFL). In one embodiment, the classification algorithm is configured to receive as an input the exhalation waveform of the breath with reduced exhalation resistance (i.e., perturbed breath) and of the breath preceding the perturbation (i.e., reference breath). That is, the classification algorithm is configured to receive as an input the reference expiratory flow-volume curve and the perturbed expiratory flow-volume curve. 
     In one embodiment, the one or more breaths preceding the perturbation breath are used to increase the robustness of the algorithm (e.g., by computing an average reference breath) and/or assessing whether the reference breath is sufficiently stable and repeatable so that its comparison with the perturbed breath is not affected by confounding factors. In one embodiment, the only factor that can change the flow waveform is the driving pressure. 
     In one embodiment, the classification algorithm is based on a single feature computed from the exhalation flow waveform or flow-volume curve. In one embodiment, the feature computed from the exhalation flow waveform or flow-volume curve includes the percentage of exhaled volume of air that occurs with the flow from the perturbed breath that is equal to the flow from the reference breath. In one embodiment, the exhalation flow-volume curve or volume waveform is computed by numerical integration of the measured exhalation flow-volume curve or flow waveform. In one embodiment, among the algorithm parameters to optimize are the threshold to determine whether the flows can be considered equal and the threshold in the percentage of exhaled volume to declare whether a breath is flow-limited or not. In one embodiment, the above-mentioned percentage is related to the automatic change in pressure required to abolish EFL. 
     In one embodiment, the classification algorithm based on multiple features computed from the exhalation flow-volume curve or exhalation flow waveform. In one embodiment, the features computed from the exhalation flow waveform or exhalation flow-volume curve include the percentage of exhaled volume with same flow (reference vs. perturbed breath), the exhaled volume (over the same time for the reference and perturbed breaths), the amplitude of the peak that typically occurs in the perturbed breath. In one embodiment, the classification algorithm is data-driven and as such it is trained on datasets that include both flow-limited and non-flow-limited breaths (i.e., machine learning), and then validated on an independent dataset (i.e., excluded from the training phase). 
     In one embodiment, as illustrated in  FIG. 7 , the input to the classification algorithm (e.g., expiratory flow limitation detection subsystem  118 ) includes the airflow waveforms/flow-volume curves from the perturbed breath and the airflow waveforms/flow-volume curves from the reference breaths (e.g., one or multiple breaths preceding the perturbed breath). In one embodiment, the airflow waveforms/flow-volume curves from the perturbed breath are sent to the classification algorithm (e.g., expiratory Flow Limitation Detection subsystem  118 ) from perturbed expiratory flow-volume curve determination subsystem  116 . In one embodiment, the airflow waveforms/flow-volume curves from the reference breaths (e.g., one or multiple breaths preceding the perturbed breath) are sent to the classification algorithm (e.g., expiratory Flow Limitation Detection subsystem  118 ) from reference expiratory flow-volume curve determination subsystem  112 . 
     In one embodiment, Expiratory Flow Limitation (EFL) abolishment subsystem  120  is configured to abolish EFL upon its detection. In one embodiment, the exhalation resistance is also changed to abolish EFL. In one embodiment, system  100  may be used for real-time detection and abolishment of EFL. In one embodiment, as will be explained in detail with respect to  FIG. 8 , one or more processors of computer system  102  are configured to automatically increase or decrease the exhalation airway pressure upon detection of EFL in order to abolish EFL. In one embodiment, system  100  is configured to specifically detect EFL and possibly to treat it. Additionally, system  100  is configured for reduction of exhalation resistance on selected breaths. 
     In one embodiment, system  100  is configured to automatically adjust the PEP therapy to abolish EFL, upon detection of EFL. In one embodiment, the set exhalation resistance is increased and the procedures are repeated after some breaths. In one embodiment, once the EFL is abolished, the procedures are repeated to confirm the absence of EFL at regular time intervals or when changes in the breathing pattern are detected. 
     The schematics shown in  FIG. 3  is only one possible embodiment. The implementation of the concept in  FIG. 3  can follow different embodiments, for instance the one in  FIG. 4 , where an additional pathway or passage for exhalation is shown. This pathway/passage has two possible configurations: i) open (resistance-free), ii) closed (infinite resistance). In one embodiment, valve  109  is used to switch form one configuration to the other configuration. In one embodiment, normally (reference breaths), the additional pathway/passage is blocked (closed valve). In one embodiment, when the expiratory flow (EF) is needed, the additional pathway/passage is opened (open valve) to by-pass the exhalation resistance (perturbed breath). 
       FIG. 5  shows an example of the technique to detect EFL.  FIG. 5  shows a graphical illustration of exemplary exhalation resistance reduction on select breaths in system  100 . In one embodiment, on select breaths, the exhalation resistance is dropped. Such breaths are referred in this patent application as perturbed breaths. 
     In one embodiment, the exhalation flow-volume curve of a perturbed breath is compared with the exhalation flow-volume curve of one or more preceding breaths (reference breaths).  FIG. 5  shows an example of exhalation resistance reduction on select breaths in system  100 . In one embodiment, on the selected breaths, the exhalation resistance is by-passed in order to cause a lower mouth pressure P mouth  during exhalation (i.e., higher expiratory drive). 
       FIG. 5  shows external pressure (e.g., measured in units of cm H 2 0) on the left hand side Y-axis of graph  502  and time (e.g., measured in units of seconds) on X-axis of graph  502 . For example, the external pressure is also referred to as the ambient pressure, P amb . As can be seen from graph  502 , the external pressure or ambient pressure, P amb  is maintained at a constant pressure of 0 cm H 2 0 for the entire time period between 20 seconds and 60 seconds (as shown in the X-axis of the graph  502 ). 
       FIG. 5  shows exhalation resistance (e.g., measured in units of cm H 2 0*s/L) on the left hand side Y-axis of graph  504  and time (e.g., measured in units of seconds) on X-axis of graph  504 . For example, the exhalation resistance is the flow resistance applied by flow resistor  110  in exhalation path  108 . Referring to graph  504 , for the time period between 20 seconds and 45 seconds, the exhalation resistance is maintained at 20 cm H 2 0*s/L. The exhalation resistance is then reduced/dropped from 20 cm H 2 0*s/L to 0 cm H 2 0*s/L at approximately the time of 45 seconds. The exhalation resistance is then increased or set back to 20 cm H 2 0*s/L thereafter. 
       FIG. 5  shows mouth pressure (e.g., measured in units of cm H 2 0) on the left hand side Y-axis of graph  506  and time (e.g., measured in units of seconds) on X-axis of graph  506 . For example, the mouth pressure is measured at a patient interface (e.g., mask or mouthpiece  111 ) and is also referred to as P mouth . Referring to graph  506 , for the time period between 20 seconds and 45 seconds, when the exhalation resistance is maintained at 20 cm H 2 0*s/L, the mouth pressure, P mouth  remained constant. When the exhalation resistance is reduced/dropped from 20 cm H 2 0*s/L to 0 cm H 2 0*s/L at approximately the time of 45 seconds, the mouth pressure, P mouth  is lowered as can be clearly seen in graph  506 . When exhalation resistance is increased or set back to 20 cm H 2 0*s/L thereafter, the mouth pressure, P mouth  is also increased to its previous value (i.e., the value of P mouth  during the time period between 20 seconds and 45 seconds. 
       FIG. 6  shows two exemplary flow comparisons between perturbed and reference breaths (flow-volume curves/loops) obtained from system  100 . 
       FIG. 6  shows flow information (e.g., measured in units of liters/second) on the X-axis of flow-volume curves  602  and  604 .  FIG. 6  also shows volume information (e.g., measured in units of liters) on the left Y-axis of flow-volume curves  602  and  604 . 
     In the left plot of  FIG. 6  or flow-volume curve  602 , an increase in expiratory drive does not cause an increase in flow. That is, the dotted line (reference expiratory flow-volume) curve and line (perturbed expiratory flow-volume) curve are very close to each other (except for the very beginning of the expiratory phase). Thus, the breath in the left plot of  FIG. 6  is flow-limited. The flow-volume curve  602  shows a flow-volume curve with the EFL. 
     In the right plot of  FIG. 6  or flow-volume curve  604 , an increase in expiratory drive causes a significantly higher exhalation flow. That is, the dotted line (reference expiratory flow-volume) curve and line (perturbed expiratory flow-volume) curve are not close to each other. Thus, the breath in the right plot of  FIG. 6  or flow-volume curve  604  is not flow-limited. The flow-volume curve  604  shows a flow-volume curve without the EFL. 
       FIG. 7  shows an example of EFL detection by reduction of exhalation resistance in system  100  and corresponding treatment to abolish EFL. In one embodiment, following detection of EFL, the expiratory pressure level is increased by increasing the exhalation resistance and the procedure (perturbation, classification algorithm and resistance update) is repeated. 
       FIG. 7  shows exhalation resistance (e.g., measured in units of cm H 2 0*s/L) on the left hand side Y-axis of graph  702  and time (e.g., measured in units of seconds) on X-axis of graph  702 . For example, the exhalation resistance is the flow resistance applied by flow resistor  110  in exhalation path  108 . Referring to graph  702 , for the time period between 0 seconds and 25 seconds, the exhalation resistance is maintained at 15 cm H 2 0*s/L. In one embodiment, the airflow waveforms/flow-volume curves from the reference breaths (e.g., one or multiple breaths preceding the perturbed breath) are sent to the classification algorithm (e.g., Expiratory Flow Limitation detection subsystem  118 ) from reference expiratory flow-volume curve determination subsystem  112 , for example, during the time period between 0 seconds and 25 seconds as shown in  FIG. 7 . 
     The exhalation resistance is then reduced or dropped from 15 cm H 2 0*s/L to 0 cm H 2 0*s/L at approximately the time of 25 seconds. In one embodiment, the airflow waveforms/flow-volume curves from the perturbed breath are sent to the classification algorithm (e.g., Expiratory Flow Limitation detection subsystem  118 ) from perturbed expiratory flow-volume curve determination subsystem  116 , for example, after the time period of 25 seconds as shown in  FIG. 7 . In one embodiment, Expiratory Flow Limitation detection subsystem  118  is configured to detect the Expiratory Flow Limitation (EFL) of the patient by comparing the determined perturbed expiratory flow-volume curve with the determined reference expiratory flow-volume curve. 
     In one embodiment, if the Expiratory Flow Limitation (EFL) of the patient is detected, the exhalation resistance is increased to, for example, 17 cm H 2 0*s/L, for example, during the time period between 32 seconds and 47 seconds as shown in  FIG. 7 . The procedures repeat thereafter. That is, for the time period between 32 seconds and 47 seconds, the exhalation resistance is maintained at 17 cm H 2 0*s/L. The exhalation resistance is then reduced or dropped from 17 cm H 2 0*s/L to 0 cm H 2 0*s/L at approximately after the time of 47 seconds. In one embodiment, the airflow waveforms/flow-volume curves from the reference breaths (e.g., one or multiple breaths preceding the perturbed breath) are sent to the classification algorithm (e.g., expiratory Flow Limitation Detection subsystem  118 ) from reference expiratory flow-volume curve determination subsystem  112 , for example, during the time period between 32 seconds and 47 seconds as shown in  FIG. 7 . In one embodiment, the airflow waveforms/flow-volume curves from the perturbed breath are sent to the classification algorithm (e.g., expiratory Flow Limitation Detection subsystem  118 ) from perturbed expiratory flow-volume curve determination subsystem  116 , for example, after the time period of 47 seconds as shown in  FIG. 7 . In one embodiment, Expiratory Flow Limitation detection subsystem  118  is configured to detect the Expiratory Flow Limitation (EFL) of the patient by comparing the determined perturbed expiratory flow-volume curve with the determined reference expiratory flow-volume curve. 
     In one embodiment, if the Expiratory Flow Limitation (EFL) of the patient is not detected, the exhalation resistance is decreased/reduced. In one embodiment, if the Expiratory Flow Limitation (EFL) of the patient is not detected, the exhalation resistance is not increased. 
       FIG. 7  also shows volume (e.g., measured in units of liters) on the left hand side Y-axis of graph  704  and time (e.g., measured in units of seconds) on X-axis of graph  704 . For example, the volume is the flow-volume information obtained from sensor  106 . 
       FIG. 8  shows a more detailed flow chart for the embodiment in  FIG. 7 .  FIG. 8  shows an example of EFL detection by exhalation resistance reduction and corresponding abolishment flow chart.  FIG. 8  is a flow chart for detecting EFL of the patient. Referring to  FIG. 8 , method  800  for detecting EFL of the patient is provided. Method  800  is implemented by computer system  102  that comprises one or more physical processors executing computer program instructions which, when executed, perform method  800 . Method  800  comprises: obtaining, from one or more sensors ( 106 ), flow-volume information of exhaled air through exhalation passage  108 ; determining, by computer system  102 , a reference expiratory flow-volume curve using flow-volume information of the exhaled air through exhalation passage  108  when a reference exhalation resistance is provided by flow resistor  110  in exhalation passage  108 ; adjusting flow resistor  110  to lower the exhalation resistance below the reference exhalation resistance; determining, by computer system  102 , a perturbed expiratory flow-volume curve using flow-volume information of the exhaled air through exhalation passage  108  when the lowered exhalation resistance is provided by flow resistor  110  in exhalation passage  108 ; and detecting, by computer system  102 , the Expiratory Flow Limitation (EFL) of the patient based on (i) the determined perturbed expiratory flow-volume curve (ii) the determined reference expiratory flow-volume curve. 
     In one embodiment, referring to  FIG. 8 , system  100  is started with a set/reference exhalation resistance at procedure  801 . In one embodiment, at procedure  802 , system  100  is continued to operate or run at the set/reference exhalation resistance, for example, for n breaths. In one embodiment, at procedure  803 , system  100  is configured to change the exhalation resistance (i.e., from the set/reference exhalation resistance to a different exhalation resistance) in exhalation passage  108  (e.g., by adjusting flow resistor  110 ) during the exhalation phase of (n+1) breath. 
     In one embodiment, at procedure  804 , system  100  is configured to change the exhalation resistance in exhalation passage  108  (e.g., by adjusting flow resistor  110 ) on exhalation phase of (n+2) breath. In one embodiment, at procedure  804 , system  100  is configured to change the exhalation resistance in exhalation passage  108  to the set/reference exhalation resistance. 
     In one embodiment, at procedure  805 , system  100  is configured to determine reference expiratory flow-volume curve using the flow-volume information of the exhaled air through exhalation passage  108  for the n breaths. In one embodiment, at procedure  805 , system  100  is also configured to determine perturbed expiratory flow-volume curve using the flow-volume information of the exhaled air through exhalation passage  108  for the n+1 breath. In one embodiment, at procedure  805 , system  100  is configured to detect the Expiratory Flow Limitation (EFL) of the patient based on (i) the determined perturbed expiratory flow-volume curve (ii) the determined reference expiratory flow-volume curve. 
     In one embodiment, at procedure  806 , if the EFL is detected, then, at procedure  807 , system  100  is configured to increase the set exhalation resistance in exhalation passage  108  (e.g., by adjusting flow resistor  110 ). In one embodiment, method  800  loops/goes back to procedure  802  after procedure  806  and method  800  repeats therefrom. 
     In one embodiment, at procedure  806 , if the EFL is not detected, then, at procedure  808 , system  100  is configured to operate at the set/reference exhalation resistance in exhalation passage  108  for n breaths. 
     In one embodiment, at procedure  809 , system  100  is configured to determine whether the EFL is detected for x consecutive times. In one embodiment, if the EFL is not detected for x consecutive times, then method  800  loops/goes back to procedure  802  after procedure  809  and method  800  repeats therefrom. 
     In one embodiment, if the EFL is detected for x consecutive times, then, at procedure  810 , system  100  is configured to reduce the set/reference exhalation resistance in exhalation passage  108  (e.g., by adjusting flow resistor  110 ). In one embodiment, method  800  loops/goes back to procedure  802  after procedure  810  and method  800  repeats therefrom. 
     In one embodiment, the patient goes to a doctor. In one embodiment, the patient&#39;s doctor asks questions about, for example, 1) history of patient&#39;s smoking; 2) exposure to secondhand smoking, air pollution, chemical or dust; 3) symptoms such as shortness of breath, chronic cough and mucus, etc. In one embodiment, the patient&#39;s doctor performs spirometry test to determine first Forced expiratory volume (FEV1) and Forced vital capacity (FVC). In one embodiment, the patient&#39;s doctor, using that information, determines whether the patient has a COPD and determines the patient&#39;s COPD stage classification. 
     In one embodiment, the patient&#39;s doctor then uses system  100  of the present patent application to detect EFL in that COPD patient. In one embodiment, the patient&#39;s doctor uses system  100  to directly assess whether the patient is affected by EFL. In one embodiment, the patient is asked by the doctor to normally breathe through system  100  in the supine position. In one embodiment, system  100  includes a resistance on exhalation path  108  that creates positive exhalation pressure (PEP). That is, in one embodiment, system  100  causes PEP by means of its exhalation resistance. In one embodiment, once the patient is comfortably breathing through system  100 , the patient&#39;s doctor presses a (manual or electronic) button that removes the exhalation resistance on exhalation path  108 . That is, after a few breaths, one breath is taken without the exhalation resistance. That is, the patient takes a few breaths at higher PEP followed by a few breaths at lower PEP. In one embodiment, the PEP may be changed manually. In one embodiment, flow is measured and flow-volume loops are used to compare consecutive breaths at different PEP. 
     In one embodiment, the patient&#39;s doctor is presented, by system  100 , flow-volume plots or curves, for example, such as shown in  FIG. 6 . That is, referring to  FIG. 6 , exhalation flow-volume loops for breaths with exhalation resistance (reference) and without exhalation resistance (perturbed) are compared. The latter corresponds to breaths with increased expiratory pressure drive. If they do not lead to increased flow, the patient is flow limited. 
     In one embodiment, the patient&#39;s doctor then prescribes vector/therapy if the patient is flow-limited. That is, if the patient&#39;s flow-volume plots are similar to that shown in the left hand side plots in  FIG. 6 , the patient&#39;s doctor determines that the patient is affected by EFL and then prescribes vector/therapy. 
     In one embodiment, system  100  includes a (transmitting) unit to transmit the measured flow information (or flow-volume curve(s)) to an external processor and/or display (e.g., smartphone, tablet or dedicated processor/display) for the clinician to analyze the flow-volume curve(s) and make the diagnosis. 
     In one embodiment, system  100  provides a portable, inexpensive device or system for the diagnosis of EFL in non-ventilated patients. In one embodiment, system  100  requires no collaboration from the patient. 
     In one embodiment, system  100  may be used for EFL screening in a doctor&#39;s office. In one embodiment, system  100  may be used for EFL monitoring at a patient&#39;s home. In one embodiment, system  100  may be used for more comfortably assessing pharmaceutical treatments. 
     In one embodiment, system  100  may be used for on-line EFL detection. In one embodiment, one or more processors of computer system  102  (e.g., running an algorithm) are configured to automatically perform changes in exhalation pressure/resistance on select breaths. In one embodiment, changes in exhalation pressure on select breaths are manually triggered by the patient. 
     In one embodiment, one or more processors of computer system  102  are configured to compute flow-volume curves. In one embodiment, one or more processors of computer system  102  are configured (e.g., by running an algorithm) for the automated classification (i.e., flow-limited vs. non-flow-limited) of the breaths corresponding to such curves. In one embodiment, the output of the algorithm (i.e., EFL or no EFL) is signaled to the patient by visual or audio signals. In one embodiment, system  100  includes a (transmitting) unit to transmit the measured flow information (or flow-volume curve(s)) for remote monitoring and/or for the patient to have access to the actual flow-volume curves processed by the classification algorithm. 
     In one embodiment, the alteration of the expiratory resistance comprises, after a plurality of breaths at reference resistance (or reference positive expiratory pressure), changing the resistance, typically to a lower level, and maintaining the new resistance (or positive expiratory pressure) for one or more breaths. In one embodiment, the expiratory resistance is continuously adjusted during the expiratory phase using feedback control and/or adaptive feed-forward control or compensation. 
     In one embodiment, a subsystem of system  100  may be configured to determine the reference exhalation resistance using previously obtained pressure information, previously obtained flow information, previously obtained exhalation resistance information, previously obtained flow-volume information and/or previously obtained EFL information from a plurality of patients. In one embodiment, this subsystem is also configured to continuously obtain subsequent pressure information, subsequent flow information, subsequent flow-volume information, subsequent exhalation resistance information, and/or subsequent EFL information of the plurality of patients. That is, the subsystem may continuously obtain subsequent information associated with the multiple patients. As an example, the subsequent information may comprise additional information corresponding to a subsequent time (after a time corresponding to information that was used to determine the EFL information). As an example, the subsequent information may be obtained from one or more monitoring devices and associated one or more sensors. 
     The subsequent information may be utilized to further update or modify the reference/set exhalation resistance (e.g., new information may be used to dynamically update or modify the reference/set exhalation resistance), etc. In some embodiments, this subsystem is configured to then continuously modify or update the reference/set exhalation resistance based on the subsequent pressure information, the subsequent flow information, subsequent flow-volume information, the subsequent exhalation resistance information, the subsequent EFL information or other subsequent information. For example, the “subsequent” information may be used in addition to the flow-volume loops (e.g., as described herein) to determine whether a patient is flow-limited. 
     In one embodiment, the present patent application provides an inexpensive (low cost) and portable system/device for the detection and treatment of EFL. In one embodiment, system  100  is portable and inexpensive (as opposed to the Forced Oscillation Technique (FOT) and Negative Expiratory Pressure (NEP) devices). In one embodiment, system  100  is a hand-held device. 
     Thanks to its simplicity, system  100  of the present patent application can be used for a wide range of applications, from screening in a doctor&#39;s office, to on-line detection of EFL on patients who are regularly using the device/system to relieve the EFL symptoms and even on-line detection combined with automatic adjustment of the device/system itself to abolish EFL. In one embodiment, system  100  of the present patent application can be used for periodic monitoring/diagnosis at home as well as continuous real-time detection and abolishment of EFL. 
     In one embodiment, system  100  is attractive because system  100  is configured to detect EFL in a direct way. That is, system  100  is configured to measure EFL according to the definition of EFL instead of relying on measurements more or less correlated to EFL (e.g., like ΔXrs and FEV1/FVC measurements, obtained via a Forced Oscillation Technique (FOT) and spirometry, respectively). 
     In one embodiment, system  100  is configured to provide direct assessment of EFL. In one embodiment, the detection by system  100  is based on the same principle of the current practice of manual abdomen compression, but it is automated to overcome variability and subjectivity of manual procedures. 
     In one embodiment, system  100  does not require patient&#39;s collaboration (as opposed to spirometry). In one embodiment, system  100  can be designed with different levels of automation to meet different needs, from screening to prolong use with detection and abolishment of EFL. 
     In one embodiment, the various computers and subsystems illustrated in  FIG. 2  may comprise one or more computing devices that are programmed to perform the functions described herein. The computing devices may include one or more electronic storages (e.g., database  132 , or other electronic storages), one or more physical processors programmed with one or more computer program instructions, and/or other components. The computing devices may include communication lines or ports to enable the exchange of information with a network (e.g., network  150 ) or other computing platforms via wired or wireless techniques (e.g., Ethernet, fiber optics, coaxial cable, WiFi, Bluetooth, near field communication, or other communication technologies). The computing devices may include a plurality of hardware, software, and/or firmware components operating together to provide the functionality attributed herein to the servers. For example, the computing devices may be implemented by a cloud of computing platforms operating together as the computing devices. 
     The electronic storages may comprise non-transitory storage media that electronically stores information. The electronic storage media of the electronic storages may include one or both of system storage that is provided integrally (e.g., substantially non-removable) with the servers or removable storage that is removably connectable to the servers via, for example, a port (e.g., a USB port, a firewire port, etc.) or a drive (e.g., a disk drive, etc.). The electronic storages may include 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. The electronic storages may include one or more virtual storage resources (e.g., cloud storage, a virtual private network, and/or other virtual storage resources). The electronic storages may store software algorithms, information determined by the processors, information received from the servers, information received from client computing platforms, or other information that enables the servers to function as described herein. 
     The processors may be programmed to provide information processing capabilities in the servers. As such, the processors may include one or more of a digital processor, an analog processor, or 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. In one embodiment, the processors may include a plurality of processing units. These processing units may be physically located within the same device, or the processors may represent processing functionality of a plurality of devices operating in coordination. The processors may be programmed to execute computer program instructions to perform functions described herein of subsystems  112 - 120  or other subsystems. The processors may be programmed to execute computer program instructions by software; hardware; firmware; some combination of software, hardware, or firmware; and/or other mechanisms for configuring processing capabilities on the processors. 
     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 present patent application has been described in 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 present patent application is not limited to the 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 patent application 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.