Patent Publication Number: US-2020297950-A1

Title: Methods and systems for adaptive base flow and leak compensation

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/358,519, entitled “METHODS AND SYSTEMS FOR ADAPTIVE BASE FLOW AND LEAK COMPENSATION,” filed on Nov. 22, 2016, which application is a continuation of U.S. patent application Ser. No. 13/341,957, now U.S. Pat. No. 9,498,589, filed on Dec. 31, 2011, the entire disclosures of which are hereby incorporated herein by reference. 
    
    
     INTRODUCTION 
     Medical ventilator systems have long been used to provide ventilatory and supplemental oxygen support to patients. These ventilators typically comprise a source of pressurized oxygen which is fluidly connected to the patient through a conduit or tubing. Further, ventilators often measure and calculate various ventilator and/or patient parameters during the ventilation of a patient. For example, patient-ventilator synchrony and spirometry are major features with significant clinical utility. Patient-ventilator synchrony ensures timely and adequate ventilator response to patient&#39;s respiratory efforts. Spirometry data provides valuable information for patient evaluation and clinical decision making. Accordingly, synchrony (i.e., appropriate triggering from exhalation into inhalation and cycling from inhalation into exhalation) and accuracy of the spirometry data is an important performance characteristic of ventilators. Leak-compensated ventilation aims to ensure optimum synchrony and spirometry data in the presence of system leak conditions. 
     Methods and Systems for Adaptive Base Flow and Leak Compensation 
     This disclosure describes systems and methods for providing adaptive base flow scheduling during ventilation of a patient to optimize patient-machine synchrony and accuracy of estimated exhaled as well as inhaled tidal volumes. Further, this disclosure describes systems and methods for providing adaptive inspiratory trigger threshold scheduling during the adaptive base flow scheduling. Further still, this disclosure describes systems and methods for determining an estimated leak flow and adjusting the adaptive base flow scheduling and the adaptive inspiratory trigger threshold scheduling based on the estimated leak flow. Moreover, this disclosure describes systems and methods for determining a change in the estimated leak flow and adjusting the adaptive base flow scheduling and the adaptive inspiratory trigger threshold scheduling based on the change in the estimated leak flow. 
     According to embodiments, a method is provided for ventilating a patient with a ventilator. The method comprises delivering a base flow to a patient during exhalation, wherein the base flow includes an estimated leak flow. Moreover, the method comprises determining an initial base flow, determining an initial inspiratory trigger threshold, and delivering the initial base flow during at least a first portion of the exhalation while setting an inspiratory trigger threshold to the initial inspiratory trigger threshold. The method further comprises changing the base flow from the initial base flow toward a desired base flow during at least a second portion of exhalation and decreasing an inspiratory trigger threshold from the initial inspiratory trigger threshold toward a desired inspiratory trigger threshold while performing the step of increasing or decreasing the base flow. Moreover, the method comprises determining a change in the estimated leak flow; and progressively adjusting the base flow in a set time period during the exhalation to compensate for the determined change in the estimated leak flow while adjusting the inspiratory trigger threshold in the set time period. 
     According to further embodiments, a ventilator system is provided comprising a pressure generating system adapted to generate a flow of breathing gas, a ventilation tubing system including a patient interface for connecting the pressure generating system to a patient, and at least one sensor operatively coupled to at least one of the pressure generating system and the ventilation tubing system. The ventilator system further comprising a leak estimation module, wherein the leak estimation module determines a change in the estimated leak flow in the ventilation tubing system by utilizing output from the at least one sensor. Furthermore, the ventilator system comprising a base flow trajectory module, wherein the base flow trajectory module delivers a base flow including the estimated leak flow during exhalation to the patient, wherein the base flow trajectory module changes the base flow delivered to the patient from an initial base flow toward a desired base flow during at least a portion of the exhalation, and wherein the base flow trajectory module progressively adjusts the base flow during a set time period during the exhalation to compensate for the determined change in the estimated leak flow. The ventilator system also comprising an inspiratory trigger threshold trajectory module, wherein the inspiratory trigger threshold trajectory module sets an inspiratory trigger threshold during exhalation, wherein the inspiratory trigger threshold trajectory module decreases the inspiratory trigger threshold from an initial inspiratory trigger threshold towards a desired inspiratory trigger threshold while the base flow trajectory module changes the base flow delivered to the patient. The ventilator system further comprising a processor in communication with the pressure generating system, the at least one sensor, the leak estimation module, the inspiratory trigger threshold trajectory module, and the base flow trajectory module. 
     According to further embodiments, a computer-readable medium having computer-executable instructions for performing a method of ventilating a patient with a ventilator is provided. The method comprising delivering a base flow to a patient during exhalation, where in the base flow includes an estimated leak flow. The method further comprising determining an initial base flow, determining an initial inspiratory trigger threshold, and delivering the initial base flow during at least a first portion of the exhalation while setting an inspiratory trigger threshold to the initial inspiratory trigger threshold. The method further comprising changing the base flow from the initial base flow toward a desired base flow during at least a second portion of exhalation and decreasing an inspiratory trigger threshold from the initial inspiratory trigger threshold toward a desired inspiratory trigger threshold while performing the step of increasing or decreasing the base flow. Moreover, the method comprising determining a change in the estimated leak flow and progressively adjusting the base flow in a set time period during the exhalation to compensate for the determined change in the estimated leak flow while adjusting the inspiratory trigger threshold in the set time period. 
     According to further embodiments, a ventilator system is provided comprising means for delivering a base flow to a patient during exhalation, where in the base flow includes an estimated leak flow. The ventilator system further comprising means for determining an initial base flow and means for determining an initial inspiratory trigger threshold. The ventilator system also comprising means for changing the base flow from an initial base flow toward a desired base flow during at least a portion of exhalation and means for decreasing the inspiratory trigger threshold from the initial inspiratory trigger threshold toward a first trigger threshold value while performing the step of increasing or decreasing the base flow. The ventilator system further comprising means for determining a change in the estimated leak flow and means for progressively adjusting the base flow in a set time period during the exhalation to compensate for the determined change in the estimated leak flow while adjusting the inspiratory trigger threshold for the set time period. 
     These and various other features as well as advantages which characterize the systems and methods described herein will be apparent from a reading of the following detailed description and a review of the associated drawings. Additional features are set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the technology. The benefits and features of the technology will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following drawing figures, which form a part of this application, are illustrative of embodiments of systems and methods described below and are not meant to limit the scope of the invention in any manner, which scope shall be based on the claims appended hereto. 
         FIG. 1  illustrates an embodiment of a ventilator. 
         FIG. 2  illustrates an embodiment of a method for ventilating a patient on a ventilator. 
         FIG. 3A  illustrates an embodiment of a first portion of a method for ventilating a patient on a ventilator. 
         FIG. 3B  illustrates an embodiment of a second portion of the method shown in  FIG. 3A  for ventilating a patient on a ventilator. 
         FIG. 4  illustrates an embodiment of a graph of delivered base flow and a set inspiratory trigger threshold over time during an exhalation. 
     
    
    
     DETAILED DESCRIPTION 
     Although the techniques introduced above and discussed in detail below may be implemented for a variety of medical devices, the present disclosure will discuss the implementation of these techniques in the context of a medical ventilator for use in providing ventilation support to a human patient. A person of skill in the art will understand that the technology described in the context of a medical ventilator for human patients could be adapted for use with other systems such as ventilators for non-human patients and general gas transport systems. 
     Medical ventilators are used to provide a breathing gas to a patient who may otherwise be unable to breathe sufficiently. In modern medical facilities, pressurized air and oxygen sources are often available from wall outlets. Accordingly, ventilators may provide pressure regulating valves (or regulators) connected to centralized sources of pressurized air and pressurized oxygen. The regulating valves function to regulate flow so that respiratory gas having a desired concentration of oxygen is supplied to the patient at desired pressures and rates. Ventilators capable of operating independently of external sources of pressurized air are also available. 
     Spirometry data provides valuable information for patient evaluation and clinical decision making. Accordingly, the accuracy of the spirometry data is an important performance characteristic of ventilators. Spirometry volumes may be calculated by integrating the net flow, which is a linear combination of flow rates measured by a number of flow sensors at both the inspiratory (delivery) side and at the exhalation (exhaust) side. These flow sensors possess different uncertainties and the overall accuracy performance is a function of a combination of the properties of individual devices. Exhaled tidal volume is measured during the expiratory phase of a ventilator breath while a base flow is delivered through the patient circuit. To determine the volume of gas inhaled or exhaled by the patient, the net flow (total delivered flow minus total flow through exhalation module) is used for integration. That is, the delivered base flow is subtracted from the sum of the base flow and patient flow exiting through the exhalation port. Delivered flow during exhalation is base flow and consists of a desired combination of appropriate gases. The flow exiting the exhalation module during the active phase of patient exhalation is the sum of base flow delivered by the ventilator and exhaled flow from the patient lung. The flow entering the patient&#39;s lung during inhalation is the algebraic sum of the total delivered flow minus the flow compressed in the tubing and any flow exiting through the exhalation module. According to embodiments, for both inhalation spirometry and exhalation spirometry, the flow (volume) lost through tubing leaks should be accounted for accordingly. The spirometry parameter of exhaled tidal volume is measured during patient&#39;s active exhalation. Therefore, the smaller the ventilator-delivered base flow is during active exhalation, the smaller the uncertainty contributed by measuring the same quantity by different sensors (once on the delivery side and a second time as a portion of exhaust gas on the exhalation side). This is particularly advantageous under neonatal conditions when tidal volumes and exhaled flow rates are relatively smaller and may be some orders of magnitude smaller than the base flow. 
     Accordingly, the systems and methods described herein provide ventilation with an adaptive base flow initiation scheduling strategy to optimize the accuracy of estimated exhaled tidal volume. However, changing base flow during exhalation may affect inspiratory triggering and may lead to a false triggering of inspiration prior to a patient desired inspiration. Accordingly, the systems and methods described herein also provide ventilation with an adaptive trigger threshold initiation scheduling strategy to prevent undesired triggering of inspiration. For example, if a change in leak size is detected just prior to or at the beginning of exhalation and a transition of base flow level is to be executed, then, during a first exhalation portion when patient-initiated triggering is unlikely, the inspiratory trigger threshold is set relatively high. However, during a second exhalation period, when patient-initiated triggering is more likely, the inspiratory trigger threshold is reduced. Therefore, as exhalation progresses or during a second portion exhalation, the inspiratory trigger threshold is decreased making it easier for a patient to initiate a desired inspiration. Similarly, if a change in leak size is detected during ongoing exhalation and a base flow transition is executed, then, during a first transitory period the inspiratory trigger threshold is adjusted appropriately to prevent false triggering during the base flow level change and subsequently adjusted towards the desired level in a smooth fashion in coordination with the smooth transition of the base flow level to its final magnitude. 
     According to embodiments, the adaptive base flow initiation scheduling strategy is further adjusted to account for estimated leak flow from the ventilation tubing circuit. For example, a change in leak flow during exhalation changes the amount of base flow the patient tubing receives, which can provide the system with too much or too little flow during exhalation. When base flow is too high, this may cause patient discomfort; whereas if the base flow is too low, this may cause inaccurate triggering. Accordingly, the adaptive base flow initiation scheduling strategy is adjusted to account for changes in the estimated leak flow detected during exhalation. Such changes in leak size, and consequently in desired base flow, may occur at the beginning of exhalation or at a certain point during the exhalation period. As discussed above, adjustments in base flow during exhalation may affect inspiratory triggering and lead to a false triggering of inspiration prior to a patient desired inspiration. Accordingly, the systems and methods described herein also provide ventilation with an adaptive trigger threshold initiation scheduling strategy that is adjusted during the time period the base flow is adjusted (i.e., according to the adaptive base flow initiation scheduling strategy) to account for detected changes in estimated leak flow to prevent undesired triggering of inspiration. 
       FIG. 1  is a diagram illustrating an embodiment of an exemplary ventilator  100  connected to a human patient  150 . Ventilator  100  includes a pneumatic system  102  (also referred to as a pressure generating system  102 ) for circulating breathing gases to and from patient  150  via the ventilation tubing system  130 , which couples the patient  150  to the pneumatic system  102  via an invasive (e.g., endotracheal tube, as shown) or a non-invasive (e.g., nasal mask) patient interface  180 . 
     Ventilation tubing system  130  (or patient circuit  130 ) may be a two-limb (shown) or a one-limb circuit for carrying gases to and from the patient  150 . In a two-limb embodiment, a fitting, typically referred to as a “wye-fitting”  170 , may be provided to couple a patient interface  180  (as shown, an endotracheal tube) to an inspiratory limb  132  and an expiratory limb  134  of the ventilation tubing system  130 . 
     Pneumatic system  102  may be configured in a variety of ways. In the present example, pneumatic system  102  includes an expiratory module  108  coupled with the expiratory limb  134  and an inspiratory module  104  coupled with the inspiratory limb  132 . Compressor  106  or other source(s) of pressurized gases (e.g., air, oxygen, and/or helium) is coupled with inspiratory module  104  and the expiratory module  108  to provide a gas source for ventilatory support via inspiratory limb  132 . 
     The inspiratory module  104  is configured to deliver gases to the patient  150  according to prescribed ventilatory settings. In some embodiments, inspiratory module  104  is configured to provide ventilation according to various breath types. 
     The expiratory module  108  is configured to release gases from the patient&#39;s lungs according to prescribed ventilatory settings. The expiratory module  108  is associated with and/or controls an expiratory valve for releasing gases from the patient  150 . Further, the expiratory module  108  may instruct the pressure generating system  102  and/or the inspiratory module  104  to deliver a base flow during exhalation. 
     The ventilator  100  may also include one or more sensors  107  communicatively coupled to ventilator  100 . The sensors  107  may be located in the pneumatic system  102 , ventilation tubing system  130 , and/or on the patient  150 . The embodiment of  FIG. 1  illustrates a sensor  107  in pneumatic system  102 . 
     Sensors  107  may communicate with various components of ventilator  100 , e.g., pneumatic system  102 , other sensors  107 , expiratory module  108 , inspiratory module  104 , processor  116 , controller  110 , trigger module  115 , inspiratory trigger trajectory module  117  (illustrated as “ITT Module”), base flow trajectory module  118  (illustrated as “Base Flow Traj. Module”), Leak Estimation Module  119  (illustrated as “Leak Est. Module), and any other suitable components and/or modules. In one embodiment, sensors  107  generate output and send this output to pneumatic system  102 , other sensors  107 , expiratory module  108 , inspiratory module  104 , processor  116 , controller  110 , trigger module  115 , inspiratory trigger trajectory module  117 , base flow trajectory module  118 , leak estimation module  119 , and any other suitable components and/or modules. 
     Sensors  107  may employ any suitable sensory or derivative technique for monitoring one or more patient parameters or ventilator parameters associated with the ventilation of a patient  150 . Sensors  107  may detect changes in patient parameters indicative of patient inspiratory or expiratory triggering, for example. Sensors  107  may be placed in any suitable location, e.g., within the ventilatory circuitry or other devices communicatively coupled to the ventilator  100 . Further, sensors  107  may be placed in any suitable internal location, such as, within the ventilatory circuitry or within components or modules of ventilator  100 . For example, sensors  107  may be coupled to the inspiratory and/or expiratory modules for detecting changes in, for example, circuit pressure and/or flow. In other examples, sensors  107  may be affixed to the ventilatory tubing or may be embedded in the tubing itself. According to some embodiments, sensors  107  may be provided at or near the lungs (or diaphragm) for detecting a pressure in the lungs. Additionally or alternatively, sensors  107  may be affixed or embedded in or near wye-fitting  170  and/or patient interface  180 . Indeed, any sensory device useful for monitoring changes in measurable parameters during ventilatory treatment may be employed in accordance with embodiments described herein. 
     As should be appreciated, with reference to the Equation of Motion, ventilatory parameters are highly interrelated and, according to embodiments, may be either directly or indirectly monitored. That is, parameters may be directly monitored by one or more sensors  107 , as described above, or may be indirectly monitored or estimated by derivation according to the Equation of Motion or other known relationships. 
     The pneumatic system  102  may include a variety of other components, including mixing modules, valves, tubing, accumulators, filters, etc. Controller  110  is operatively coupled with pneumatic system  102 , signal measurement and acquisition systems, and an operator interface  120  that may enable an operator to interact with the ventilator  100  (e.g., change ventilator settings, select operational modes, view monitored parameters, etc.). 
     In one embodiment, the operator interface  120  of the ventilator  100  includes a display  122  communicatively coupled to ventilator  100 . Display  122  provides various input screens, for receiving clinician input, and various display screens, for presenting useful information to the clinician. In one embodiment, the display  122  is configured to include a graphical user interface (GUI). The GUI may be an interactive display, e.g., a touch-sensitive screen or otherwise, and may provide various windows and elements for receiving input and interface command operations. Alternatively, other suitable means of communication with the ventilator  100  may be provided, for instance by a wheel, keyboard, mouse, or other suitable interactive device. Thus, operator interface  120  may accept commands and input through display  122 . 
     Display  122  may also provide useful information in the form of various ventilatory data regarding the physical condition of a patient  150 . The useful information may be derived by the ventilator  100 , based on data collected by a processor  116 , and the useful information may be displayed to the clinician in the form of graphs, wave representations, pie graphs, text, or other suitable forms of graphic display. For example, patient data may be displayed on the GUI and/or display  122 . Additionally or alternatively, patient data may be communicated to a remote monitoring system coupled via any suitable means to the ventilator  100 . In some embodiments, the display  122  may illustrate a minimum exhalation flow, a minimum exhalation time, a maximum exhalation time, a desired base flow, a desired inspiratory trigger, an inspiratory trigger, a base flow, an exhalation flow, an estimated leak flow, an exhalation pressure, and/or any other information known, received, or stored by the ventilator  100 . 
     In some embodiments, controller  110  includes memory  112 , one or more processors  116 , storage  114 , and/or other components of the type commonly found in command and control computing devices. Controller  110  may further include an inspiratory trigger trajectory module  117 , a base flow trajectory module  118 , a trigger module  115 , and/or a leak estimation module  119  as illustrated in  FIG. 1 . In alternative embodiments, the inspiratory trigger trajectory module  117 , the base flow trajectory module  118 , trigger module  115 , and/or the leak estimation module  119  are located in other components of the ventilator  100 , such as in the pressure generating system  102  (also known as the pneumatic system  102 ). 
     The memory  112  includes non-transitory, computer-readable storage media that stores software that is executed by the processor  116  and which controls the operation of the ventilator  100 . In an embodiment, the memory  112  includes one or more solid-state storage devices such as flash memory chips. In an alternative embodiment, the memory  112  may be mass storage connected to the processor  116  through a mass storage controller (not shown) and a communications bus (not shown). Although the description of computer-readable media contained herein refers to a solid-state storage, it should be appreciated by those skilled in the art that computer-readable storage media can be any available media that can be accessed by the processor  116 . That is, computer-readable storage media includes non-transitory, volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information such as computer-readable instructions, data structures, program modules or other data. For example, computer-readable storage media includes RAM, ROM, EPROM, EEPROM, flash memory or other solid state memory technology, CD-ROM, DVD, or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by the computer. 
     The base flow trajectory module  118  determines the amount of base flow to deliver to the patient circuit tubing during exhalation. The base flow trajectory module  118  adjusts the base flow based on an estimated leak flow during exhalation. The base flow trajectory module  118  receives the estimated leak flow from another component of the ventilator  100 , such as the controller  110 , processor  116 , and/or the leak estimation module  119 . 
     The base flow trajectory module  118  delivers a constant base flow during a first portion of exhalation and then varies the base flow delivered during at least a part of a second portion of exhalation. Accordingly, the base flow trajectory module  118  determines an initial base flow to deliver during a first portion of exhalation. In some embodiments, the initial base flow is input or selected by the operator. In other embodiments, the initial base flow is determined by the ventilator  100  based on the configuration of the ventilator  100  and/or based on ventilator and/or patient parameters and settings. The first portion of exhalation includes at least the beginning or start of the exhalation period. In some embodiments, the first portion of exhalation is a minimum exhalation time. The “minimum exhalation time” as referred to herein is a predetermined amount of time in which it is unlikely that a patient would desire to begin inspiration or would attempt to trigger an inspiration. The base flow trajectory module  118  instructs the inspiratory module  104  to deliver the initial base flow at the beginning of inhalation. In further embodiments, the base flow trajectory module  118  delivers the initial base flow at the beginning of the first portion of exhalation or for the entire duration of the first portion of exhalation. 
     The base flow trajectory module  118  may also determine a desired base flow. In some embodiments, the desired base flow is input or selected by the operator. In other embodiments, the desired base flow is determined by the ventilator  100  based on the configuration of the ventilator  100  and/or based on ventilator and/or patient parameters. 
     The base flow trajectory module  118  instructs the inspiratory module  104  to change the delivered base flow from the initial base flow towards a first flow value, such as the desired base flow, during at least a second portion of exhalation. The second portion of exhalation does not overlap with the first portion of exhalation. Accordingly, the second portion of exhalation does not include the beginning of exhalation, but may begin immediately thereafter. 
     The second portion of exhalation starts or begins based on the occurrence of a condition. The base flow trajectory module  118  may determine the occurrence of the condition based on output received from sensors  107 . Accordingly, in some embodiments, the base flow trajectory module  118  instructs the inspiratory module  104  to change the base flow from the initial base flow towards the desired base flow after determining the occurrence of a condition. In some embodiments, the condition includes determining that a minimum exhalation time has expired, determining that a monitored exhalation flow is below the minimum exhalation flow; determining that the monitored exhalation flow is below the minimum exhalation flow prior to expiration of a maximum exhalation time, and/or determining that the maximum exhalation time has expired. In other embodiments, the condition includes determining that a minimum exhalation time has expired and determining that either a monitored exhalation flow is below the minimum exhalation flow prior to expiration of a maximum exhalation time or the maximum exhalation time has expired. The maximum exhalation time is a predetermined amount of time after which it becomes highly likely that a patient would attempt to trigger inspiration. The minimum exhalation flow is a predetermined flow rate that when exhaled by the patient indicates that a patient is approaching the end of active exhalation. In some embodiments, the base flow trajectory module  118  instructs the inspiratory module  104  to change the delivered base flow from the initial base flow towards a first flow value at the start of a second portion of exhalation or, according to some embodiments, for the entire duration of the second portion exhalation. 
     In embodiments, the base flow trajectory module  118  instructs the inspiratory module  104  to change the base flow according to an exponential trajectory. In some embodiments, the exponential trajectory is based on a time constant that is indicative of the expected response time from the initial point to the final desired flow target. The time constant may be determined by the ventilator  100  based on the ventilator configuration or based on ventilator and/or patient parameters. In other embodiments, the time constant is input or selected by the operator. 
     In further embodiments, the base flow trajectory module  118  instructs the inspiratory module  104  to change the base flow until the delivered base flow is essentially or substantially the first flow value, such as a desired base flow. Once the delivered base flow substantially reaches the first flow value, the base flow trajectory module  118  instructs the inspiratory module  104  to deliver the first flow value. The first flow value is substantially reached or essentially reached when the ventilator  100  can no longer change the amount of base flow provided without reaching or exceeding the first flow value based on the sensitivity and precision of the ventilator components. 
     According to embodiments, if a change in leak size (leak flow rate) is detected during the exhalation phase (e.g., past the initial restricted period), the base flow should be adjusted accordingly. In this case, the base flow trajectory module  118  instructs the inspiratory module  104  to change the base flow in a sooth fashion (e.g., exponential ascend or descend) towards the desired level. In such cases, the duration of the transition as well as the initial magnitude for adjusting the trigger sensitivity is determined by the timeline of the transition of the base flow and the status of the patient&#39;s exhalation activity (e.g., the higher the patient&#39;s expiratory effort, the lower the probability of a new breath trigger). 
     Ventilators  100 , depending on their mode of operation, may trigger automatically and/or in response to a detected change in a ventilator and/or patient parameter. The trigger module  115  receives and/or determines one or more inspiratory trigger thresholds. In some embodiments, the trigger module  115  receives an inspiratory trigger threshold from the ITT Module  117 . In other embodiments, the trigger module  115  determines an inspiratory trigger threshold based on ventilator and/or patient parameters and/or the ventilator configuration. For example, the ventilator may be preconfigured to deliver an inspiration after a predetermined amount of exhalation time to prevent a patient from becoming under-ventilated. In other embodiments, the trigger module  115  receives an inspiratory trigger threshold from operator input or selection. 
     During exhalation, the trigger module  115  monitors ventilator and/or patient parameters and compares these parameters to one or more inspiratory trigger thresholds to determine if the parameters meet and/or exceed the inspiratory trigger thresholds. Sensors  107  suitable for this detection may include any suitable sensing device as known by a person of skill in the art for a ventilator  100 . If the trigger module  115  determines that ventilator and/or patient parameters meet and/or exceed an inspiratory trigger threshold during exhalation, the trigger module  115  instructs the inspiratory module  104  to deliver an inspiration, which effectively ends the exhalation phase controlled by the expiratory module  108 . If the trigger module  115  determines that ventilator and/or patient parameters do not meet and/or exceed an inspiratory trigger threshold during exhalation, the trigger module  115  continues to monitor the ventilator and/or patient parameters and compare them to a trigger threshold until the ventilator and/or patient parameters meet and/or exceed a trigger threshold. 
     In some embodiments, the trigger module  115  of the ventilator  100  detects changes in a ventilator and/or patient parameter via the monitoring of a respiratory gas pressure, the monitoring of lung flow, direct or indirect measurement of nerve impulses, or any other suitable method for detecting changes in a ventilator parameter for comparison to an inspiratory trigger threshold. In embodiments where changes in a ventilator parameter are detected by monitoring flow and/or pressure, the sensitivity of the ventilator  100  to changes in pressure and/or flow, may be adjusted. For example, the lower a pressure or flow change trigger threshold setting, the more sensitive the ventilator  100  may be to a patient initiated trigger. However, each ventilator  100  will have a minimum measurable inspiratory flow and thereby have a change in flow that the ventilator  100  cannot detect. Accordingly, a monitored parameter below a minimum measurable value will not be detected by the ventilator  100 . 
     According to an embodiment, a pressure-triggering method may involve the trigger module  115  of the ventilator  100  monitoring the circuit pressure, and detecting a slight drop in circuit pressure. The slight drop in circuit pressure may indicate that the patient&#39;s respiratory muscles are creating a slight negative pressure that in turn generates a pressure gradient between the patient&#39;s lungs and the airway opening in an effort to inspire. The ventilator  100  may interpret the slight drop in circuit pressure as a patient trigger and may consequently initiate inspiration by delivering respiratory gases. 
     Alternatively, the trigger module  115  of the ventilator  100  may detect a flow-triggered event. Specifically, the trigger module  115  of the ventilator  100  may monitor the circuit flow, as described above. If the ventilator  100  detects a slight drop in the base flow through the exhalation module during exhalation, this may indicate that the patient  150  is attempting to inspire. In this case, the ventilator  100  is detecting a drop in base flow attributable to a slight redirection of gases into the patient&#39;s lungs (in response to a slightly negative pressure gradient as discussed above). Accordingly, changes in base flow as instructed by the base flow trajectory module  118  may, if the trigger threshold is set too low, trigger an unwanted inspiration. 
     The inspiratory trigger trajectory module  117  (illustrated as the “ITT Module”) determines a patient initiated inspiratory trigger threshold. The ITT module  117  sends the determined inspiratory trigger threshold to another component of the ventilator, such as the controller  110 , processor  116 , and/or the trigger module  115 . The trigger module  115 , as discussed above, monitors the ventilator and/or patient parameters to determine if the parameters meet and/or exceed the inspiratory trigger threshold. The ITT module  117  continuously updates the inspiratory trigger threshold. Accordingly, the ITT module  117  may send different inspiratory trigger thresholds during different portions of exhalation. 
     The ITT module  117  determines and sets an initial inspiratory trigger threshold while delivering the initial base flow. In some embodiments, the initial inspiratory trigger threshold is input or selected by the operator. In other embodiments, the initial inspiratory trigger threshold is determined by the ventilator  100  based on the configuration of the ventilator and/or based on ventilator parameters and/or patient parameters. The initial inspiratory trigger is set during at least the first portion of exhalation, which includes at least the beginning or start of the exhalation period. 
     In some embodiments, in order to prevent undesirable early inspiratory triggers, the inspiratory trigger may be set relatively high. For example, in some embodiments, the initial inspiratory trigger requires a change of flow of at least 6 liters per minute (LPM). In other embodiments, the initial inspiratory trigger requires a change of flow of at least 8 LPM. In further embodiments, the initial inspiratory trigger requires a change of flow of at least 10 LPM. 
     However, as the exhalation continues the likelihood that a patient desires to initiate an inspiration increases. Accordingly, the ITT module  117  decreases an inspiratory trigger threshold during the second portion of exhalation. The decrease in the inspiratory trigger threshold requires the patient to make less of an effort to trigger a desired inspiration during the second portion of exhalation. Thus, the ITT module  117  decreases an inspiratory trigger threshold while the base flow trajectory module  118  changes the base flow delivered to the patient circuit tubing, as illustrated in  FIG. 4 . 
     In some embodiments, the ITT module  117  decreases the inspiratory trigger at an exponential trajectory. In some embodiments, the exponential trajectory is based on a time constant. The time constant may be determined by the ventilator  100  based on the ventilator configuration or based on ventilator and/or patient parameters. In other embodiments, the time constant is input or selected by the operator. In some embodiments, the time constant utilized by the ITT module  117  is the same time constant utilized by the base flow trajectory module  118  to determine how to change the amount of base flow delivered to the patient circuit tubing. In other embodiments, the ITT module  117  decreases an inspiratory trigger threshold as a function of the amount the base flow trajectory module  118  changes base flow or instructs the inspiratory module  104  to change base flow. In further embodiments, the ITT module  117  decreases an inspiratory trigger threshold concurrently while the base flow trajectory module  118  changes the base flow delivered to the patient circuit tubing, as illustrated in  FIG. 4  (illustrating an increase in base flow concurrently with a decrease in the inspiratory trigger threshold). 
     In some embodiments, the ITT module  117  also determines a first inspiratory trigger threshold value, such as a desired inspiratory trigger threshold. In some embodiments, the first inspiratory trigger threshold value is input or selected by the operator. In other embodiments, the first inspiratory trigger threshold value is determined by the ventilator  100  based on the configuration of the ventilator  100  and/or based on ventilator parameters and/or patient parameters. In embodiments with a first inspiratory trigger threshold value, the ITT module  117  decreases the inspiratory trigger threshold from the initial inspiratory trigger threshold towards the first inspiratory trigger threshold value, such as a desired inspiratory trigger threshold. 
     Accordingly, in some embodiments, the ITT module  117  decreases the inspiratory trigger threshold until the inspiratory trigger essentially or substantially reaches the first inspiratory trigger threshold value. Once the inspiratory trigger threshold substantially reaches the first inspiratory trigger threshold value, the ITT module  117  sets the inspiratory trigger threshold value to the first inspiratory trigger threshold value. The first inspiratory trigger threshold value is substantially reached or essentially reached when the ventilator  100  can no longer decrease the inspiratory trigger threshold without reaching or passing the first inspiratory trigger threshold value based on the sensitivity and precision of the ventilator components. 
     According to some embodiments, the base flow trajectory module  118  allows the ventilator  100  to provide a lower base flow during a first portion of exhalation and a higher base flow during a second portion of exhalation or vice versa. When the ventilator delivers a lower base flow during active exhalation (i.e., the first portion of exhalation), there is less uncertainty caused by measuring base flow at different sensors  107  (once on the delivery side and a second time as a portion of exhaust gas on the exhalation side). This is particularly advantageous under neonatal conditions when tidal volumes and exhaled flow rates are relatively smaller and may be some orders of magnitude smaller than the base flow. Accordingly, the base flow trajectory module  118  allows the processor  116  or controller  110  to more accurately calculate exhaled tidal volume and/or spirometry than ventilators that utilize a constant base flow or a higher amount of base-flow during active exhalation. 
     The leak estimation module  119  estimates the amount of flow leaking from the ventilation tubing system  130 . The leak estimation module  119  sends the estimated leak flow to other components of the ventilator  100 , such as the controller  110 , processor  116 , base flow trajectory module  118 , pneumatic system  102 , and/or display  122 . 
     According to embodiments, the initial base flow includes the estimated leak flow determined by leak estimation module  119 . In some embodiments, the initial base flow is zero if there is no estimated leak flow and no desired initial base flow. In alternative embodiments, the initial base flow is at least equivalent to or greater than the estimated leak flow. The leak estimation module  119  estimates the amount of flow leaking from the ventilation tubing system  130  by utilizing any conventionally known method for estimating leak flow from the ventilation tubing system  130 . Additionally, with reference to embodiments described above, the first flow value includes the estimated leak flow as determined by the leak estimation module  119  to compensate for the amount of flow lost from the ventilation tubing system  130  during ventilation. Moreover, according to embodiments, the base flow trajectory module  118  utilizes the estimated leak flow, as determined by the leak estimation module  119 , to determine the initial base flow and/or the first flow value. 
     Further, the leak estimation module  119  determines if there has been a change in the estimated leak flow during exhalation. In some embodiments, after a change in the estimated leak flow has been detected, the leak estimation module  119  updates the estimated leak flow based on the detected change. In embodiments, the leak estimation module  119  determines if there has been a change in the estimated leak flow during exhalation by monitoring one or more patient and/or ventilator parameters or settings. In further embodiments, the leak estimation module  119  determines if there has been a change in the estimated leak flow during exhalation by monitoring output from one or more sensors  107 . The leak estimation module  119  determines a change in the amount of flow leaking from the ventilation tubing system  130  during exhalation by utilizing any conventionally known method for estimating leak flow and/or for detecting a change in the leak flow from the ventilation tubing system  130 . The leak estimation module  119  sends the determined change in the estimated leak flow (or an updated estimated leak flow value) to other components of the ventilator  100 , such as the controller  110 , processor  116 , base flow trajectory module  118 , ITT module  117 , pneumatic system  102 , and/or display  122 . 
     According to embodiments, a change in leak flow during exhalation can impact the base flow during exhalation, resulting in too much or too little base flow during exhalation and causing patient discomfort and/or inaccurate triggering. Accordingly, the determined change in estimated leak flow is utilized by the base flow trajectory module  118  to adjust the base flow during exhalation. For example, if an increase in estimated leak flow is detected during exhalation, base flow may be increased. Alternatively, if a decrease in the estimated leak flow is detected during exhalation, base flow may be decreased. 
     According to further embodiments, when the base flow trajectory module  118  receives a determined change in the estimated leak flow, the base flow trajectory module  118  progressively adjusts the base flow delivered during exhalation during a set time period to compensate for the determined change. The base flow trajectory module  118  may increase or decrease the delivered base flow during exhalation depending upon the determined change in the estimated leak flow. As used herein “progressively adjust” refers to changing the base flow delivered in a plurality of increments during a set time period to compensate for the detected change in estimated leak flow. For example, the base flow trajectory module  118  may change the amount of base flow delivered over the set time period in phases, in a step-wise pattern, and/or utilizing an exponential trajectory. 
     In some embodiments, the base flow is progressively adjusted utilizing an exponential trajectory based on a time constant. The time constant may be the same time constant utilized by the ventilator during the second phase of exhalation to change the delivered base flow and/or to decrease the inspiratory trigger threshold. In some embodiments, the ventilator determines the time constant. In other embodiments, the time constant is selected or input by an operator. 
     In alternative embodiments, the base flow is progressively adjusted as a function of the determined change in the estimated leak flow. In some embodiments, the base flow is progressively adjusted based on percentage multiplied by the determined change in the estimated leak flow, such as a percentage of 5%, 10%, 15%, 20%, 25%, etc. For example, if the estimated leak flow increases by 5 liters per min (LPM), the base flow trajectory module  118  may progressively adjust the base flow delivered during exhalation during the set time period by 10% increments, e.g., progressively increase the delivered base flow by increments of 0.50 LPM over the set time period until the base flow is increased by the 5 LPM increase in estimated leak flow. 
     In some embodiments, the set time period is determined by the ventilator  100 . In some embodiments, the set time period is based on the configuration of the ventilator. In other embodiments, the set time period is determined by the ventilator based on ventilator and/or patient parameters or settings. In some embodiments, the set time period determined by the ventilator is a function of the determined change in the estimated leak flow. In alternative embodiments, the set time period is selected or input by the operator. Is some embodiments, the set time period is 200 milliseconds (ms) or less. In other embodiments, the set time period is 150 ms or less. In other embodiments, the set time period is 125 ms or less. 
     When the ITT module  117  receives a determined change in the estimated leak flow, the ITT module  117  adjusts the inspiratory trigger threshold for the set time period. For example, if the estimated leak flow increases (resulting in a decreased base flow through the exhalation module), the inspiratory trigger threshold may also be increased, thereby decreasing trigger sensitivity and making it less probable for a false determination of the patient inspiratory trigger. Alternatively, if the estimated leak flow decreases (resulting in an increase in base flow through the exhalation module), the inspiratory trigger threshold may also be decreased for a transition period, thereby increasing the probability of detecting the patient&#39;s effort to trigger inspiration. 
     In some embodiments, the inspiratory trigger threshold is increased based on a function of a detected increase in estimated leak flow. In this case, according to embodiments, the inspiratory trigger is increased one time by a set amount for the duration of the set time period. In alternative embodiments, the ITT module  117  progressively increases the inspiratory trigger threshold for the set time period. As used herein “progressively increases” refers to increasing the inspiratory trigger threshold in a plurality of increments during the set time period. For example, the ITT module  117  may increase the inspiratory trigger threshold during the set time period in phases, in a step-wise pattern, and/or by utilizing an exponential trajectory. 
     In further embodiments, the inspiratory trigger threshold is progressively increased utilizing an exponential trajectory based on a time constant. The time constant may be the same time constant utilized by the ventilator during the second phase of exhalation to increase the delivered base flow and/or to decrease the inspiratory trigger threshold. In some embodiments, the ventilator determines the time constant. In other embodiments, the time constant is selected or input by an operator. 
     In some embodiments, the inspiratory trigger threshold is increased based on a percentage multiplied by the determined increase in the estimated leak flow, such as a percentage of 5%, 10%, 15%, 20%, 25%, etc. For example, if the estimated leak flow increases by 5 liters per minute (LPM) (decreasing base flow), the ITT module  117  may increase the inspiratory trigger threshold by 10% increments over a set time period during exhalation, e.g., 0.5 LPM each cycle, until the inspiratory trigger threshold is increased by 5 LPM. According to embodiments, the ITT module  117  may increase the inspiratory trigger threshold according to any suitable percentage, algorithm, protocol, etc. 
     According to alternative embodiments, the inspiratory trigger threshold is decreased as a function of a detected decrease in estimated leak flow. In this case, the inspiratory trigger may be decreased one time by a set amount for the duration of the set time period. In alternative embodiments, the ITT module  117  progressively decreases the inspiratory trigger threshold for the set time period. As used herein “progressively decreases” refers to decreasing the inspiratory trigger threshold in a plurality of increments during the set time period. For example, the ITT module  117  may decrease the inspiratory trigger threshold during the set time period in phases, in a step-wise pattern, and/or by utilizing an exponential trajectory. 
     In further embodiments, the inspiratory trigger threshold is progressively decreased utilizing an exponential trajectory based on a time constant. The time constant may be the same time constant utilized by the ventilator during the second phase of exhalation to change the delivered base flow and/or to decrease the inspiratory trigger threshold. In some embodiments, the ventilator determines the time constant. In other embodiments, the time constant is selected or input by an operator. 
     In some embodiments, the inspiratory trigger threshold is decreased based on a percentage multiplied by the determined decrease in the estimated leak flow, such as a percentage of 5%, 10%, 15%, 20%, 25%, etc. For example, if the estimated leak flow decreases by 5 liters per minute (LPM) (decreasing base flow), the ITT module  117  may decrease the inspiratory trigger threshold by 10% increments over a set time period during exhalation, e.g., 0.5 LPM each cycle, until the inspiratory trigger threshold is decreased by 5 LPM. According to embodiments, the ITT module  117  may decrease the inspiratory trigger threshold according to any suitable percentage, algorithm, protocol, etc. 
     According to alternative embodiments, during a second portion of exhalation, the ITT Module  117  decreases the inspiratory trigger threshold when the base flow is changed. During the second portion of exhalation, it is more likely that the patient will trigger a desired inspiration. As such, decreasing the inspiratory trigger threshold increases trigger sensitivity and makes it easier for the patient to trigger inspiration. According to additional embodiments, ITT Module  117  adaptively adjusts the inspiratory trigger threshold during the second period of exhalation based on detecting a change in estimated leak flow. That is, while the inspiratory trigger threshold may follow a generally declining exponential trajectory during the second portion of exhalation, this declining exponential may be adjusted based on detecting a change in the estimated leak flow (i.e., increasing the inspiratory trigger threshold upon detecting an increase in estimated leak flow and decreasing the inspiratory trigger threshold upon detecting a decrease in estimated leak flow during the second portion of exhalation). 
       FIG. 2  illustrates an embodiment of a method  200  for ventilating a patient with a ventilator. Method  200  begins at the start of exhalation. During exhalation the ventilator delivers a base flow to a patient. The base flow includes an estimated leak flow. According to embodiments, during a first portion of exhalation the ventilator delivers an initial base flow to the patient circuit tubing. According to further embodiments, during a second portion of exhalation, the ventilator delivers an adaptive base flow that changes exponentially from the initial base flow toward a desired base flow. Additionally, during exhalation the ventilator determines and sets an inspiratory trigger threshold. For example, during exhalation the ventilator determines an initial inspiratory trigger threshold and a desired inspiratory trigger threshold. According to embodiments, during a first portion of exhalation the ventilator sets an initial inspiratory trigger threshold. According to further embodiments, during a second portion of exhalation the ventilator configures the inspiratory trigger threshold to decrease exponentially from the initial inspiratory trigger threshold toward a desired inspiratory trigger threshold. 
     As illustrated, method  200  includes a first portion delivery operation  202 . According to embodiments, the first portion of exhalation includes at least the beginning or start of exhalation and does not overlap with a second portion of exhalation. In some embodiments, the first portion of exhalation includes a minimum exhalation time. 
     According to embodiments, the ventilator delivers an initial base flow to the patient at the start of or for the entire duration of a first portion of exhalation during first portion delivery operation  202 . The initial base flow includes an estimated leak flow. According to embodiments, the initial base flow may be predetermined by the ventilator based on the configuration of the ventilator or determined by the ventilator based on ventilator and/or patient parameters or settings. In an alternative embodiment, the initial base flow may be input or selected by an operator. According to further embodiments, the initial base flow is automatically adjusted to account for an estimated leak flow. According to embodiments, an amount of flow is added to the estimated leak flow in order to determine the initial base flow. According to embodiments, the amount of flow added may be predetermined by the ventilator based on the configuration of the ventilator or may be determined by the ventilator based on ventilator and/or patient parameters or settings. In an alternative embodiment, the amount of flow added to the estimated leak flow to determine the initial base flow is input or selected by an operator. 
     According to additional embodiments, the ventilator during the first portion delivery operation  202  determines an initial inspiratory trigger threshold for the first portion of exhalation. According to embodiments, the initial inspiratory trigger threshold may be predetermined by the ventilator based on the configuration of the ventilator or determined by the ventilator based on ventilator and/or patient parameters or settings. In an alternative embodiment, the initial inspiratory trigger threshold may be input or selected by an operator. 
     In some embodiments, the initial base flow is a base flow of zero or close to zero when the estimated leak flow is zero or close to zero. In alternative embodiments, the initial base flow is at least equivalent to or greater than the estimated leak flow. In some embodiments, the initial inspiratory trigger threshold is set relatively high. During early exhalation it is unlikely that a patient actually desires to trigger an inspiration. Accordingly, to prevent monitored parameters from resulting in a false trigger of an undesired inspiration, a high initial inspiratory trigger threshold may be utilized. For example, the initial inspiratory trigger threshold may require a change of flow of at least 6 to 10 LPM. 
     As illustrated, method  200  includes a change in estimated leak flow decision operation  203  (illustrated as “Change in Est. Leak Flow?”). The ventilator during the change in estimated leak flow decision operation  203  determines if there has been a change in the estimated leak flow. The ventilator monitors patient and/or ventilator parameters to determine if there has been a change in the estimated leak flow during exhalation. The estimated leak flow may be estimated by utilizing any known suitable methods or systems. 
     In some embodiments, method  200  detects changes in a ventilator and/or patient parameter via monitoring of a respiratory gas pressure, the monitoring of lung flow, direct or indirect measurement of nerve impulses, or any other suitable method for detecting changes in a ventilator and/or patient parameters. Method  200  may utilize sensors to monitor the ventilator and/or patient parameters. Sensors may include any suitable sensing device as known by a person of skill in the art for a ventilator. In some embodiments, the ventilator monitors the ventilator and/or patient parameters every computational cycle (e.g., 2 milliseconds, 5 milliseconds, 10 milliseconds, etc.) during the delivery of exhalation to determine if estimated leak flow has changed during exhalation. 
     If the ventilator during change in estimated leak flow decision operation  203  determines that there has been a change in the estimated leak flow, the ventilator selects to perform adjust operation  205 . If the ventilator during change in estimated leak flow decision operation  203  determines that there has not been a change in the estimated leak flow, the ventilator selects to perform transition condition decision operation  204 . 
     Method  200  also includes an adjust operation  205 . The ventilator during adjust operation  205  progressively adjusts the initial base flow during a set time period during exhalation to compensate for the determined change in the estimated leak flow while also adjusting the inspiratory trigger threshold for the set time period. For example, if the ventilator determines estimated leak flow has increased (insufficient initial base flow), the ventilator may increase the initial base flow to compensate for the increase in estimated leak flow. Alternatively, if the ventilator determines estimated leak flow has decreased (excessive initial base flow), the ventilator may decrease the initial base flow to compensate for the decrease in estimated leak flow. In some embodiments, after a change in the estimated leak has been detected, ventilator during the adjust operation  205  further estimates the updated estimated leak flow based on the detected change during exhalation. 
     According to embodiments, the ventilator during adjust operation  205  may increase or decrease the initial base flow during exhalation depending on the determined change in the estimated leak flow. As used herein “progressively adjusted” refers to incrementally changing the initial base flow delivered during a set time period over a plurality of control cycles (e.g., 2 ms control cycles, 5 ms control cycles, etc.) to compensate for the detected change in estimated leak flow. For example, the ventilator during adjust operation  205  may change the amount of initial base flow delivered during the set time period in phases, in a step-wise pattern, and/or utilizing an exponential trajectory. The set time period for adjusting the initial base flow may be determined by the ventilator, e.g., based on pre-established ventilator settings or based on ventilator calculations. In alternative embodiments, the set time period is selected or input by the operator. In some embodiments, as described above, the initial base flow is progressively adjusted (increased or decreased) utilizing an exponential trajectory based on a time constant. In other embodiments, the initial base flow is adjusted (increased or decreased) based on a percentage multiplied by the determined change in the estimated leak flow, such as a percentage of 5%, 10%, 15%, 20%, 25%, etc. According to embodiments, the initial base flow may be increased according to any suitable percentage, algorithm, protocol, etc. 
     In additional embodiments, during adjust operation  205  the initial inspiratory trigger threshold is adjusted (increased or decreased) as a function of the detected change (increase or decrease) in estimated leak flow. For example, if the ventilator determines estimated leak flow has increased (decreasing the initial base flow), the ventilator may increase the initial inspiratory trigger threshold to compensate for the increase in estimated leak flow. In this case, the trigger sensitivity is decreased making it more difficult for the patient to trigger inspiration. Alternatively, if the ventilator determines estimated leak flow has decreased (increasing the initial base flow), the ventilator may decrease the initial inspiratory trigger threshold to compensate for the decrease in estimated leak flow. In this case, the trigger sensitivity is increased making it easier for the patient to trigger inspiration. 
     According to further embodiments, the ventilator during adjust operation  205  may increase or decrease the initial inspiratory trigger threshold during exhalation depending on the determined change in the estimated leak flow. As used herein “progressively adjusted” refers to incrementally changing the initial inspiratory trigger threshold delivered during a set time period over a plurality of control cycles (e.g., 2 ms control cycles, 5 ms control cycles, etc.) to compensate for the detected change in estimated leak flow. For example, the ventilator during adjust operation  205  may change the initial inspiratory trigger threshold during the set time period in phases, in a step-wise pattern, and/or utilizing an exponential trajectory. The set time period for adjusting the initial base flow may be determined by the ventilator or selected or input by the operator. In some embodiments, as described above, the initial inspiratory trigger threshold is progressively adjusted (increased or decreased) utilizing an exponential trajectory based on a time constant. In other embodiments, the initial inspiratory trigger threshold is adjusted (increased or decreased) based on a percentage multiplied by the determined change in the estimated leak flow, such as a percentage of 5%, 10%, 15%, 20%, 25%, etc. According to embodiments, the initial inspiratory trigger threshold may be increased according to any suitable percentage, algorithm, protocol, etc. 
     Further, method  200  includes a transition condition decision operation  204  (illustrated as “transition condition?”). During the transition condition decision operation  204 , the ventilator determines if a condition has been met. The condition may include any suitable condition, including determining that a minimum exhalation time has expired, determining that an exhalation flow is below the minimum exhalation flow, determining that the exhalation flow is below the minimum exhalation flow prior to expiration of a maximum exhalation time, and/or determining that the maximum exhalation time has expired. The first portion of exhalation ends when the condition has been met. The second portion of exhalation begins when the condition has been met. 
     According to embodiments, if the ventilator during transition condition decision operation  204  determines that a condition has been met, the ventilator selects to perform second portion delivery operation  206 . If the ventilator during transition condition decision operation  204  determines that a condition has not been met, the ventilator selects to perform inspiratory trigger decision operation  209 . 
     According to embodiments, during the second portion delivery operation  206 , the ventilator changes (i.e., increases or decreases) the base flow delivered to the patient tubing from the initial base flow toward a desired base flow during the second portion of exhalation. According to embodiments, the desired base flow is received via input or selection by an operator, e.g., via a graphical user interface, keyboard, mouse, and/or any other suitable input device for receiving and interpreting operator commands, instructions, and/or selections. In an alternative embodiment, the desired base flow is determined by the ventilator. 
     In some embodiments, the ventilator changes base flow from the initial base flow toward the desired base flow at the start of or during the entire duration of the second portion of exhalation. According to alternative embodiments, the ventilator incrementally changes the base flow from the initial base flow toward the desired base flow over a period of time. For example, the ventilator may incrementally change the base flow from the initial base flow toward the desired base flow in phases, in a step-wise pattern, and/or by utilizing an exponential trajectory. That is, the ventilator may incrementally change the base flow from the initial base flow toward the desired base flow to a first flow value in a first control cycle and to a second flow value in a second control cycle, etc. 
     In some embodiments, the ventilator during second portion delivery operation  206  changes the base flow from the initial base flow toward the desired base flow until the desired base flow is reached or substantially reached. If the delivered base flow reaches or substantially reaches the desired base flow, the ventilator during second portion delivery operation  206  delivers the desired base flow until inspiration is triggered by the patient. In some embodiments, the ventilator during second portion delivery operation  206  changes the base flow according to an exponential trajectory. In further embodiments, the ventilator during second portion delivery operation  206  changes the base flow according to an exponential trajectory based on a time constant. The time constant may be determined by the ventilator or input or selected by an operator. 
     Further, during the second portion delivery operation  206 , the ventilator decreases an inspiratory trigger threshold from the initial inspiratory trigger threshold toward a desired inspiratory trigger threshold during at least a portion of the second portion of exhalation. Accordingly, in some embodiments, the ventilator concurrently or simultaneously changes the delivered base flow as the ventilator lowers the inspiratory trigger threshold during the second portion delivery operation  206 . 
     In some embodiments, the ventilator during second portion delivery operation  206  decreases the inspiratory trigger threshold from the initial inspiratory trigger threshold towards the desired inspiratory trigger threshold until the desired inspiratory trigger threshold is reached or substantially reached. If the inspiratory trigger threshold reaches or substantially reaches the desired inspiratory trigger threshold, the ventilator during second portion delivery operation  206  maintains the inspiratory trigger threshold at the desired inspiratory trigger threshold until the patient triggers inspiration. 
     According to embodiments, the ventilator during second portion delivery operation  206  decreases the inspiratory trigger threshold at the start of or during the entire duration of the second portion of exhalation. According to alternative embodiments, the ventilator incrementally decreases the inspiratory trigger threshold from the initial inspiratory trigger threshold towards the desired inspiratory trigger threshold over a period of time. For example, the ventilator may incrementally decrease the inspiratory trigger threshold from the initial inspiratory trigger threshold towards the desired inspiratory trigger threshold in phases, in a step-wise pattern, and/or by utilizing an exponential trajectory. That is, the ventilator may incrementally decrease the inspiratory trigger threshold from the initial inspiratory trigger threshold towards the desired inspiratory trigger threshold to a first flow value in a first control cycle and to a second flow value in a second control cycle, etc. 
     In some embodiments, the ventilator during second portion delivery operation  206  decreases the inspiratory trigger threshold according to an exponential trajectory. In further embodiments, the ventilator during second portion delivery operation  206  decreases the inspiratory trigger threshold at an exponential trajectory based on a time constant. In some embodiments, the time constant is determined by the ventilator or input or selected by an operator. In further embodiments, the time constant may be the same time constant utilized by the ventilator to determine the amount to change the delivered base flow. In additional embodiments, the ventilator during second portion delivery operation  206  decreases the inspiratory trigger threshold as a function of the amount the ventilator changes the delivered base flow. 
     In some embodiments, the ventilator may decrease the inspiratory trigger threshold from the initial inspiratory trigger threshold towards the desired inspiratory trigger threshold until the desired inspiratory trigger threshold is substantially reached. If the set inspiratory trigger threshold reaches or substantially reaches the desired inspiratory trigger threshold, the ventilator during second portion delivery operation  206  maintains the inspiratory trigger threshold at the desired inspiratory trigger threshold until the patient triggers inspiration. 
     That is, method  200  decreases the inspiratory trigger threshold while the base flow is being changed. According to embodiments, the longer the exhalation period, the more likely the patient will attempt to initiate an inspiratory trigger. As such, decreasing the inspiratory trigger threshold during the second portion of exhalation allows a patient to exert less effort to trigger a desired inspiration when it becomes more likely that a patient will attempt to trigger an inspiration. 
     As illustrated, method  200  includes a change in estimated leak flow decision operation  207  (illustrated as “Change in Est. Leak Flow?”). Change in estimated leak flow decision operation  207  is substantially that same as change in estimated leak flow decision operation  203 , described above. That is, at change in estimated leak flow decision operation  207  the ventilator determines if there has been a change in the estimated leak flow via any suitable means. 
     If the ventilator during change in estimated leak flow decision operation  207  determines that there has been a change in the estimated leak flow, the ventilator selects to perform adjust operation  208 . If the ventilator during change in estimated leak flow decision operation  207  determines that there has not been a change in the estimated leak flow, the ventilator selects to perform detect inspiratory trigger decision operation  210 . 
     At adjust operation  208 , the ventilator progressively adjusts the base flow during a set time period during the second period of exhalation to compensate for the determined change in the estimated leak flow. For example, if the ventilator determines estimated leak flow has increased (insufficient base flow), the ventilator may increase the base flow to compensate for the increase in estimated leak flow. Alternatively, if the ventilator determines estimated leak flow has decreased (excessive base flow), the ventilator may decrease the base flow to compensate for the decrease in estimated leak flow. According to embodiments, during the second portion of exhalation, base flow is adjusted from an initial base flow to a desired base flow while also being adjusted based on detecting a change in estimated leak flow. 
     Additionally, during adjust operation  208  the ventilator progressively adjusts the inspiratory trigger threshold during the set time period to compensate for the determined change in the estimated leak flow. For example, if the ventilator determines estimated leak flow has increased (insufficient base flow), the ventilator may increase the inspiratory trigger threshold to compensate for the increase in estimated leak flow. Alternatively, if the ventilator determines estimated leak flow has decreased (excessive base flow), the ventilator may decrease the inspiratory trigger threshold to compensate for the decrease in estimated leak flow. According to embodiments, during the second portion of exhalation, inspiratory trigger threshold is adjusted from an initial inspiratory trigger threshold to a desired inspiratory trigger threshold while also being adjusted based on detecting a change in estimated leak flow. 
     As illustrated, method  200  includes an inspiratory trigger decision operation  209  (illustrated as “Detect Insp. Trigger?”). During the inspiratory trigger decision operation  209 , the ventilator determines if an inspiratory trigger has been detected. Inspiratory trigger decision operation  209  is performed during the first portion of exhalation. 
     The ventilator, during inspiratory trigger decision operation  209 , monitors patient and/or ventilator parameters or settings to determine if an inspiratory trigger threshold has been met and/or exceeded during the first portion of exhalation. The inspiratory trigger threshold includes any suitable condition or threshold for determining that inspiration should be provided to the patient. During the first portion of exhalation, the inspiratory trigger threshold includes the initial inspiratory trigger threshold as determined by first portion delivery operation  202 . 
     In some embodiments, method  200  detects changes in a ventilator and/or patient parameter via the monitoring of a respiratory gas pressure, the monitoring of lung flow, direct or indirect measurement of nerve impulses, or any other suitable method for detecting changes in a ventilator parameter for comparison to inspiratory trigger thresholds. Method  200  may utilize sensors to monitor the ventilator and/or patient parameters. Sensors may include any suitable sensing device as known by a person of skill in the art for a ventilator. In some embodiments, the inspiratory trigger threshold may be a change in exhalation pressure or a change in exhalation flow. In some embodiments, the sensors are located in the pneumatic system, the breathing circuit, and/or at the patient. In some embodiments, the ventilator monitors the exhalation flow and/or exhalation pressure every computational cycle (e.g., 2 milliseconds, 5 milliseconds, 10 milliseconds, etc.) during the delivery of exhalation to determine if the inspiratory trigger threshold has been met and/or exceeded. 
     If the ventilator during inspiratory trigger decision operation  209  determines that the ventilator and/or patient parameters do not meet or exceed an inspiratory trigger threshold, the ventilator selects to perform first portion delivery operation  202 . If the ventilator during inspiratory trigger decision operation  209  determines that the ventilator and/or patient parameters do meet or exceed an inspiratory trigger threshold, the ventilator selects to perform inhale operation  211 . The performance of the inhale operation  211  ends the exhalation phase. 
     Method  200  includes an inspiratory trigger decision operation  210  (illustrated as “Detect Insp. Trigger?”). During the inspiratory trigger decision operation  210 , similar to inspiratory trigger decision operation  208 , the ventilator determines if an inspiratory trigger has been detected. Inspiratory trigger decision operation  210  is performed during the second portion of exhalation. 
     The ventilator, during inspiratory trigger decision operation  210 , monitors patient and/or ventilator parameters or settings to determine if an inspiratory trigger threshold has been met and/or exceeded during the second portion of exhalation. The inspiratory trigger threshold includes any suitable condition or threshold for determining that inspiration should be provided to the patient. During the second portion of exhalation, the inspiratory trigger threshold includes an inspiratory trigger threshold substantially equal to or declining toward the desired inspiratory trigger threshold as determined by second portion delivery operation  206 . 
     If the ventilator during inspiratory trigger decision operation  210  determines that the ventilator and/or patient parameters do not meet or exceed an inspiratory trigger threshold, the ventilator selects to perform second portion delivery operation  206 . If the ventilator during inspiratory trigger decision operation  210  determines that the ventilator and/or patient parameters do meet or exceed an inspiratory trigger threshold, the ventilator selects to perform inhale operation  211 . The performance of the inhale operation  211  ends the exhalation phase. 
     In additional embodiments, method  200  includes a display operation. The ventilator during the display operation displays any suitable information for display on a ventilator. In one embodiment, the display operation displays at least one of a minimum exhalation flow, a minimum exhalation time, a maximum exhalation time, a desired base flow, an initial base flow, a desired inspiration trigger threshold, an initial inspiratory trigger threshold, an exhalation flow, an estimated leak flow, and an exhalation pressure. 
     Accordingly, in some embodiments, method  200  further includes a calculation operation. The ventilator during the calculation operation calculates an exhaled tidal volume. The ventilator may utilize any known methods for calculating exhaled tidal volume. In some embodiments, the ventilator during the calculation operation also calculates spirometry. In some embodiments, the spirometry calculation is based on the calculated exhaled tidal volume. The ventilator may utilize any known methods for calculating spirometry. 
     In some embodiments, a microprocessor-based ventilator that accesses a computer-readable medium having computer-executable instructions for performing the method of ventilating a patient with a medical ventilator is disclosed. This method includes repeatedly performing the steps disclosed in method  200  above and/or as illustrated in  FIG. 2 . 
     In some embodiments, the ventilator system includes: means for determining an initial base flow; means for determining an initial inspiratory trigger threshold; means for delivering the initial base flow during at least a first portion of exhalation while setting the inspiratory trigger threshold to the initial inspiratory trigger threshold; means for changing base flow from the initial base flow toward a first flow value during at least a second portion of exhalation; and means for decreasing the inspiratory trigger threshold from the initial inspiratory trigger threshold toward a first trigger threshold value while performing the step of changing the base flow. 
     As should be appreciated, the particular steps and methods described herein are not exclusive and, as will be understood by those skilled in the art, the particular ordering of steps as described herein is not intended to limit the method, e.g., steps may be performed in differing order, additional steps may be performed, and disclosed steps may be excluded without departing from the spirit of the present methods. 
       FIGS. 3A and 3B  illustrate an embodiment of a method  300  for ventilating a patient with a ventilator. As illustrated, method  300  begins at the start of exhalation. As illustrated in  FIG. 3A , method  300  includes an initial base flow deliver operation  302 , determine initial inspiratory trigger threshold operation  303 , decision operation  304  (illustrated as “Detect Initial Insp. Trigger”), decision operation  306  (illustrated as “Min. Exh. Time Expired?”), decision operation  308  (illustrated as “Max. Exh. Time Expired?”), and decision operation  312  (illustrated as “Exh. Flow less than Max. Exh. Flow?”). During the initial base flow deliver operation  302 , the ventilator delivers an initial base flow to the patient during exhalation during at least a first portion of exhalation. During the initial base flow deliver operation  302 , the ventilator performs determine initial inspiratory trigger threshold operation  303 , decision operation  304 , decision operation  306 , decision operation  308 , and decision operation  312 . 
     The ventilator during the determine initial inspiratory trigger threshold operation  303 , determines an initial inspiratory trigger threshold for the first portion of exhalation. In some embodiments, initial inspiratory trigger threshold is determined by the ventilator. In other embodiments, initial inspiratory trigger threshold is determined based on operator input or selection. 
     The ventilator during the decision operation  304  monitors patient and/or ventilator parameters to determine if an inspiratory trigger threshold has been met and/or exceeded during the first portion of exhalation. The inspiratory trigger threshold includes any suitable condition or threshold for determining that inspiration should be provided to the patient. During the first portion of exhalation, the inspiratory threshold includes the initial inspiratory trigger threshold as determined by determine initial inspiratory trigger threshold operation  303 . For example, the initial inspiratory trigger threshold may require a change of pressure of at least 6 to 10 cm of H 2 O. 
     In some embodiments, method  300  detects changes in a ventilator and/or patient parameter during the decision operation  304  via the monitoring of a respiratory gas pressure, the monitoring of lung flow, direct or indirect measurement of nerve impulses, or any other suitable method for detecting changes in a ventilator parameter for comparison to inspiratory trigger thresholds. Method  300  may utilize sensors to monitor the ventilator and/or patient parameters. Sensors may include any suitable sensing device as known by a person of skill in the art for a ventilator. In some embodiments, the inspiratory trigger threshold may be a change in exhalation pressure or a change in exhalation flow. In some embodiments, the sensors are located in the pneumatic system, the breathing circuit, and/or on the patient. In some embodiments, the ventilator monitors the exhalation flow and/or exhalation pressure every computational cycle (e.g., 2 milliseconds, 5 milliseconds, 10 milliseconds, etc.) during the delivery of exhalation to determine if the inspiratory trigger threshold has been met and/or exceeded. 
     The ventilator during decision operation  304  compares the output of the one or more sensors to at least one inspiratory trigger threshold. If the output meets and/or exceeds the one or more inspiratory trigger thresholds, the ventilator determines during decision operation  304  that an inspiratory trigger is detected. If the output does not meet the one or more inspiratory trigger thresholds, the ventilator determines during decision operation  304  that an inspiratory trigger is not detected. If the ventilator determines that the inspiratory trigger is detected during the decision operation  304 , the ventilator selects to perform deliver inspiratory operation  326  (illustrated as “Deliver Insp. Operation”). If the ventilator determines that the inspiratory trigger is not detected during the decision operation  304 , the ventilator selects to perform decision operation  306 . 
     As illustrated in  FIG. 3A , method  300  includes a deliver inspiration operation  326 . The ventilator during deliver inspiration operation  326  delivers inspiration to the patient ending exhalation. The ventilator performs deliver inspiration operation  326  when a patient trigger is detected. The ventilator delivers an inspiration based on ventilator parameters, patient parameters, and/or input or selections from the operator. For example, the inspiration provided by the ventilator may be based on a selected breath type and/or mode of ventilation. 
     The ventilator during decision operation  306  determines if the minimum exhalation time has expired. As discussed above, the minimum exhalation time refers to a predetermined amount of time in which it is unlikely that a patient would desire to begin inspiration or would attempt to trigger an inspiration. If the ventilator determines that the minimum exhalation time has not expired during decision operation  306 , the ventilator selects to perform decision operation  304 . If the ventilator determines that the minimum exhalation time has expired during decision operation  306 , the ventilator selects to perform decision operation  308 . In some embodiments, the ventilator determines if the minimum exhalation time has expired by monitoring the output of sensors and/or by monitoring calculations based on the output of sensors. 
     The ventilator during decision operation  308  determines if the maximum exhalation time has expired. As discussed above, the maximum exhalation time refers to a predetermined amount of time after which it becomes highly likely that a patient would attempt to trigger inspiration. If the ventilator determines that the maximum exhalation time has not expired during decision operation  308 , the ventilator selects to perform decision operation  312 . If the ventilator determines that the maximum exhalation time has expired during decision operation  308 , the ventilator selects to perform increasing base flow delivery operation  310  (illustrated as “Incr. Base Flow Deliver Operation). In some embodiments, the ventilator determines if the maximum exhalation time has expired by monitoring the output of sensors and/or by monitoring calculations based on the output of sensors. 
     The ventilator during decision operation  312  determines if the exhalation flow is below the minimum exhalation flow. In some embodiments, the ventilator determines the exhalation flow by monitoring the output of sensors and/or by monitoring calculations based on the output of sensors. The minimum exhalation flow refers to a predetermined flow rate that when exhaled by the patient indicates that a patient is approaching the end of active exhalation. In some embodiments, the minimum exhalation flow is zero. In some embodiments, the minimum exhalation flow is determined by the ventilator. In other embodiments, the minimum exhalation flow is set or determined by the operator via operator input or selection. If the ventilator determines that the exhalation flow is below the minimum exhalation flow during decision operation  312 , the ventilator selects to perform increasing base flow delivery operation  310 . If the ventilator determines that the exhalation flow is not below the minimum exhalation flow during decision operation  312 , the ventilator selects to perform decision operation  304 . 
     As further illustrated in  FIG. 3A , method  300  includes an increasing base flow delivery operation  310  (illustrated as “Incr. Base Flow Deliver Operation). The ventilator during the increasing base flow delivery operation  310  increases the amount of base flow delivered to the patient during exhalation at an exponential trajectory from the initial base flow towards a desired base flow. The exponential trajectory is based on a constant. The constant is determined by the ventilator. In some embodiments, the desired base flow is determined by the ventilator. In other embodiments, the desired base flow is received by the ventilator via operator input or selection. 
     The increasing base flow delivery operation  310  is performed by the ventilator during at least a second portion of exhalation. During the increasing base flow delivery operation  310 , the ventilator performs decreasing inspiratory trigger threshold operation  314  (illustrated as “Decr. Insp. Trigger Operation”), decision operation  316  (illustrated as “Insp. Trigger Reach Desired Insp. Trigger?”), decision operation  318  (illustrated as “Base Flow reach Desired Base Flow?”), and decision operation  324  (illustrated as “Detect Insp. Trigger?”) as illustrated in  FIG. 3B . 
     As illustrated in  FIG. 3B , method  300  includes a decreasing inspiratory trigger threshold operation  314 . The ventilator during the decreasing inspiratory trigger threshold operation  314  decreases the inspiratory trigger threshold monitored by the ventilator during exhalation at an exponential trajectory from the initial inspiratory trigger threshold towards a desired inspiratory trigger threshold. The exponential trajectory is based on the same constant as utilized by the ventilator during the increasing base flow delivery operation  310  to determine the base flow trajectory. In some embodiments, the desired inspiratory trigger threshold is determined by the ventilator. In other embodiments, the desired inspiratory trigger threshold is received by the ventilator via operator input or selection. As discussed above the ventilator performs decreasing inspiratory trigger threshold operation  314  while performing the increasing base flow delivery operation  310 . In some embodiments, the increasing base flow delivery operation  310  is performed concurrently with the decreasing inspiratory trigger threshold operation  314  by the ventilator as illustrated in  FIG. 4 . 
     Method  300  includes a decision operation  316 , decision operation  318 , and decision operation  324 . The order of the performance of the decision operation  316 , the decision operation  318 , and decision operation  324  is irrelevant. Accordingly, the decision operation  316 , the decision operation  318 , and decision operation  324  may be performed in any order, simultaneously, at different times, and/or at overlapping times. Further, the decision operation  316 , the decision operation  318 , and decision operation  324  are all performed during at least the second portion of exhalation. 
     The ventilator during decision operation  316  determines if the inspiratory trigger threshold has substantially reached the desired inspiratory threshold. The ventilator may determine if the inspiratory trigger threshold has substantially reached a desired inspiratory threshold. If the ventilator determines that the inspiratory trigger threshold has substantially reached the desired inspiratory threshold during decision operation  316 , the ventilator selects to perform maintaining desired inspiratory trigger threshold operation  322  (illustrated as “Maintain Desired Insp. Trigger Operation”). If the ventilator determines that the inspiratory trigger threshold has not substantially reached the desired inspiratory threshold during decision operation  316 , the ventilator selects to perform decision operation  318 . 
     Further, method  300  includes a maintaining desired inspiratory trigger threshold operation  322 . The ventilator during the maintaining desired inspiratory trigger threshold operation  322  sets and holds the inspiratory trigger threshold at the desired inspiratory trigger threshold. The performance of the maintaining desired inspiratory trigger threshold operation  322  ends the ventilator performance of the decreasing inspiratory trigger threshold operation  314 . 
     The ventilator during decision operation  318  determines if the delivered base flow has substantially reached the desired base flow. The ventilator may determine if the base flow has substantially reached the desired base flow by monitoring the output of one or more sensors or by monitoring calculations based on the output of one or more sensors. If the ventilator determines that the base flow has substantially reached the desired base flow during decision operation  318 , the ventilator selects to perform desired base flow deliver operation  320 . If the ventilator determines that the base flow has not substantially reached the desired base flow during decision operation  318 , the ventilator selects to perform decision operation  324 . As discussed above, the desired inspiratory trigger threshold or the desired base flow is substantially reached when the ventilator can no longer increase the amount of base flow provided without reaching or exceeding the desired base flow or when ventilator can no longer decrease the inspiratory trigger threshold without reaching or exceeding the desired inspiratory trigger threshold based on the sensitivity and precision of the ventilator components. 
     As illustrated in  FIG. 3B , method  300  includes a desired base flow deliver operation  320 . The ventilator during the desired base flow deliver operation  320  sets and holds the base flow delivered to the patient during at the second portion of exhalation at the desired base flow. The performance of the desired base flow deliver operation  320  ends the ventilator performance of the increasing base flow delivery operation  310 . 
     Method  300  includes a decision operation  324 . The ventilator during the decision operation  324  monitors patient and/or ventilator parameters to determine if an inspiratory trigger threshold has been met and/or exceeded during the second portion of exhalation. The inspiratory trigger threshold includes any suitable condition or threshold for determining that inspiration should be provided to the patient. During the second portion of exhalation, the inspiratory threshold includes the varying inspiratory trigger threshold as determined by decreasing inspiratory trigger threshold operation  314 . 
     In some embodiments, method  300  detects changes in a ventilator and/or patient parameter during the decision operation  324  via the monitoring of a respiratory gas pressure, the monitoring of lung flow, direct or indirect measurement of nerve impulses, or any other suitable method for detecting changes in a ventilator parameter for comparison to inspiratory trigger thresholds. Method  300  may utilize sensors to monitor the ventilator and/or patient parameters. Sensors may include any suitable sensing device as known by a person of skill in the art for a ventilator. In some embodiments, the inspiratory trigger threshold may be a change in exhalation pressure or a change in exhalation flow. In some embodiments, the sensors are located in the pneumatic system, the breathing circuit, and/or on the patient. In some embodiments, the ventilator monitors the exhalation flow and/or exhalation pressure every computational cycle (e.g., 2 milliseconds, 5 milliseconds, 10 milliseconds, etc.) during the delivery of exhalation to determine if the inspiratory trigger threshold has been met and/or exceeded. 
     The ventilator during decision operation  324  compares the output of the one or more sensors to at least one inspiratory trigger threshold. If the output meets and/or exceeds the one or more inspiratory trigger threshold, the ventilator determines during decision operation  324  that an inspiratory trigger is detected. If the output does not meet the one or more inspiratory trigger thresholds, the ventilator determines during decision operation  324  that an inspiratory trigger is not detected. If the ventilator determines that the inspiratory trigger is detected during the decision operation  324 , the ventilator selects to perform deliver inspiration operation  326  (illustrated as “Deliver Insp. Operation”). If the ventilator determines that the inspiratory trigger is not detected during the decision operation  324 , the ventilator selects to perform increasing base flow delivery operation  310  as illustrated in  FIG. 3A . 
     In some embodiments, method  300  includes an estimating operation and an adjusting operation. The ventilator during the estimating operation estimates the amount of flow leaked from a ventilation tubing system during ventilation. The ventilator may utilize any known methods for estimating the amount of flow leaked from the ventilation tubing system. The ventilator during the adjusting operation adds the estimated amount of leak flow to the initial base flow to account for the amount of flow leaked from the ventilation tubing system. Further, the ventilator during the adjusting operation may add the estimated amount of leak flow to a desired base flow to account for the amount of flow leaked from the ventilation tubing system. 
     In other embodiments, method  300  includes a display operation. The ventilator during the display operation displays any suitable information for display on a ventilator. In one embodiment, the display operation displays at least one of a minimum exhalation flow, a minimum exhalation time, a maximum exhalation time, a desired base flow, a desired inspiratory trigger threshold, an inspiratory trigger threshold, a base flow, an exhalation flow, an estimated leak flow, and an exhalation pressure. 
     Method  300  decreases the inspiratory trigger threshold while the base flow is being adjusted since the longer the exhalation period, the more likely the patient will attempt to initiate an inspiratory trigger. The decrease in the inspiratory trigger threshold allows a patient to exert less effort to trigger a desired inspiration during the second portion of exhalation as it becomes more likely that a patient will attempt to trigger an inspiration. 
     Further, method  300  allows the ventilator to reduce the amount of base flow delivered during exhalation. The smaller the ventilator-delivered base flow is during active exhalation, the smaller the uncertainty contributed by measuring base flow by different sensors (once on the delivery side and a second time as a portion of exhaust gas on the exhalation side). This is particularly advantageous under neonatal conditions when tidal volumes and exhaled flow rates are relatively smaller and may be some orders of magnitude smaller than the base flow. Accordingly, method  300  allows the ventilator to more accurately calculate exhaled tidal volume and/or spirometry than ventilators that utilize a constant base flow or a higher amount of base-flow during active exhalation. 
     Accordingly, in some embodiments, method  300  includes a calculation operation. The ventilator during the calculation operation calculates an exhaled tidal volume. The ventilator may utilize any known methods for calculating exhaled tidal volume. In some embodiments, the ventilator during the calculation operation also calculates spirometry. In some embodiments, the spirometry calculation is based on the calculated exhaled tidal volume. The ventilator may utilize any known methods for calculating spirometry. 
     In other embodiments, a microprocessor-based ventilator that accesses a computer-readable medium having computer-executable instructions for performing the method of ventilating a patient with a ventilator is disclosed. This method includes repeatedly performing the steps disclosed in method  300  above and/or as illustrated in  FIG. 3 . 
     EXAMPLES 
     Example 1 
       FIG. 4  illustrates an embodiment of a graph of delivered base flow and an inspiratory trigger threshold over time during an exhalation. According to this embodiment, a base flow change is executed at the beginning of the exhalation phase. In this embodiment, the desired inspiratory trigger threshold is 3 LPM and the desired base flow is 4.5 LPM. In this embodiment, the first portion of exhalation ends upon the occurrence of a condition, which starts the second portion of exhalation. According to the illustrated embodiment, the condition occurs at 350 milliseconds (ms). The condition may include determining that a minimum exhalation time has expired, determining that an exhalation flow is below the minimum exhalation flow, determining that the exhalation flow is below the minimum exhalation flow prior to expiration of a maximum exhalation time, and/or determining that the maximum exhalation time has expired. 
     In an embodiment as illustrated in  FIG. 4 , an initial inspiratory trigger threshold of 10 LPM is set during the first portion of exhalation. As illustrated in  FIG. 4 , an initial base flow of 1.5 LPM is delivered during the first portion of exhalation. After the occurrence of the condition and during the second portion of exhalation, as illustrated in  FIG. 4 , the inspiratory trigger threshold is decreased exponentially while the delivered base flow is increased exponentially to reach 4.5 LPM. The inspiratory trigger threshold is decreased until the set inspiratory trigger threshold reaches the desired inspiratory trigger threshold (3 LPM). Once the inspiratory trigger threshold reaches the desired inspiratory trigger threshold, the inspiratory trigger threshold is maintained at the desired inspiratory trigger threshold. Further, the delivered base flow is increased until the delivered base flow reaches the desired base flow. Once the delivered base flow reaches the desired base flow, the delivered base flow is maintained at the desired base flow. 
     A patient initiated inspiration is not detected during the exhalation time shown in  FIG. 4 . If an inspiratory trigger was detected, inspiration would be delivered upon detection ending the exhalation period. 
     Example 2 
     Example 2 illustrates an embodiment of a pseudo code for the systems and methods of the disclosure. The pseudo code illustrated below utilizes an algorithm that incorporates the following aspects:
     1) Base flow is initiated after the flow rate being exhaled by the patient has reduced to a minimum threshold, which indicates that a patient is approaching the end of active exhalation;   2) Base flow will be delivered in accordance with an exponential trajectory to reach a desired base flow within an optimum interval to both maintain Positive End-Expiratory Pressure (PEEP) and to minimize false triggering; and   3) An inspiratory trigger threshold will be adaptively adjusted (with an exponential trajectory) from a less sensitive threshold (i.e., harder to trigger) at the start of exhalation phase and decreasing smoothly to asymptote to a desired inspiratory trigger threshold by the end of active exhalation or after allowing an optimum interval concomitant with reaching the final base flow.
 
The pseudo code embodiment utilizing the algorithm described above is listed below:
   

     
       
         
           
               
             
               
                   
               
             
            
               
                 //initialize 
               
               
                 filteredSensEx (inspiratory trigger threshold) = 10.0 LPM 
               
               
                 //calculate a new base flow reference: 
               
               
                 leakAdd = estimated Value (estimated leak from the ventilator tubing 
               
               
                 system); 
               
               
                 DesiredFlow = BaseFlow + leakAdd; 
               
               
                 MinQE (minimum exhalation flow) = 1.5 LPM; 
               
               
                 MinTE (minimum exhalation time) = 150 ms; 
               
               
                 Alpha (a constant) = 0.05; 
               
               
                 MaxTE (maximum exhalation time) = 500 ms; 
               
               
                 //every control cycle during exhalation phase execute the following. 
               
               
                 IF (neonatal) 
               
               
                 { 
               
            
           
           
               
               
            
               
                   
                 IF (ExhTime &lt; MinTE) 
               
            
           
           
               
            
               
                 { 
               
            
           
           
               
               
            
               
                   
                 DesiredFlow = leakAdd; 
               
               
                   
                 BaseFlowCheck = false; 
               
               
                   
                 filteredBaseFlow = 0; 
               
            
           
           
               
            
               
                 Sensitivity = setSensitivity+filteredSensEx; 
               
               
                 } 
               
               
                 Else 
               
               
                 {  IF (((Qexh &lt; MinQE) AND (!BaseFlowCheck)) OR (exhTime &gt; 
               
               
                 MaxTE)) 
               
            
           
           
               
               
            
               
                   
                 BaseFlowCheck = true; 
               
            
           
           
               
            
               
                 } 
               
            
           
           
               
               
            
               
                   
                 IF (BaseFlowCheck) 
               
            
           
           
               
               
            
               
                   
                 { 
               
            
           
           
               
               
            
               
                   
                 filteredBaseFlow = filteredBaseFlow * (1-alpha) + alpha * 
               
               
                   
                 baseFlow; 
               
               
                   
                 DesiredFlow = filteredBaseFlow + leakAdd; 
               
               
                   
                 Sensitivity = setSensitivity + filteredSenEx * (1-alpha); 
               
               
                   
                 filteredSensEx = filteredSensEx * (1-alpha) 
               
            
           
           
               
               
            
               
                   
                 } 
               
            
           
           
               
               
            
               
                   
                 Else 
               
            
           
           
               
            
               
                 { 
               
            
           
           
               
               
            
               
                   
                 DesiredFlow = leakAdd; 
               
            
           
           
               
               
            
               
                   
                  } 
               
            
           
           
               
            
               
                 } 
               
               
                 // no change if Adult or Pediatric settings. 
               
               
                   
               
            
           
         
       
     
     Example 3 
     Example 3 illustrates an embodiment of a pseudo code for the systems and methods of the disclosure. The pseudo code illustrated below utilizes an algorithm that incorporates the following aspects:
     1) Base flow is initiated and regulated based on a current estimate of the leak rate as exemplified above;   2) An increase in leak rate is detected requiring adjustment of base flow; and   3) An inspiratory trigger threshold will be adaptively adjusted (with an exponential trajectory) smoothly to asymptote to a desired inspiratory trigger threshold by the end of transition period or after allowing an optimum interval concomitant with reaching the final base flow.
 
The pseudo code embodiment utilizing the algorithm described above is listed below upon detecting a change in leak rate:
   

                                //initialize       filteredSensEx (inspiratory trigger threshold) = 5.0 LPM       //calculate new base flow and sensitivity references:       OldLeakAdd = previous estimated Value (estimated leak from the       ventilator tubing system);       NewLeakAdd = current estimated Value (updated estimated leak);       filteredBaseFlow = BaseFlow +OldLeakAdd;       DesiredBaseFlow = BaseFlow +NewLeakAdd;       Sensitivity = setSensitivity+filteredSensEx;       Alpha (a constant) = 0.05;       //Upon detecting a change in leak rate during exhalation and doing the       initialization above, perform the following every control cycle.       IF (Exhalation)       {                         filteredBaseFlow = filteredBaseFlow * (1-alpha) + alpha *           NewBaseFlow;           DesiredBaseFlow = filteredBaseFlow;           Sensitivity = setSensitivity + filteredSenEx * (1-alpha);           filteredSensEx = filteredSensEx * (1-alpha);                 }                    
The pseudo code provided above is not meant to be limiting. Further, while values are provided in the embodiment of the pseudo code above, these values are not meant to be limiting and may vary based on ventilator and/or patient parameters.
 
     Those skilled in the art will recognize that the methods and systems of the present disclosure may be implemented in many manners and as such are not to be limited by the foregoing exemplary embodiments and examples. In other words, functional elements being performed by a single or multiple components, in various combinations of hardware and software or firmware, and individual functions, can be distributed among software applications at either the client or server level or both. In this regard, any number of the features of the different embodiments described herein may be combined into single or multiple embodiments, and alternate embodiments having fewer than or more than all of the features herein described are possible. Functionality may also be, in whole or in part, distributed among multiple components, in manners now known or to become known. Thus, myriad software/hardware/firmware combinations are possible in achieving the functions, features, interfaces and preferences described herein. Moreover, the scope of the present disclosure covers conventionally known manners for carrying out the described features and functions and interfaces, and those variations and modifications that may be made to the hardware or software firmware components described herein as would be understood by those skilled in the art now and hereafter. 
     Numerous other changes may be made which will readily suggest themselves to those skilled in the art and which are encompassed in the spirit of the disclosure and as defined in the appended claims. While various embodiments have been described for purposes of this disclosure, various changes and modifications may be made which are well within the scope of the present invention. Numerous other changes may be made which will readily suggest themselves to those skilled in the art and which are encompassed in the spirit of the disclosure and as defined in the claims.