Abstract:
A ventilator for use by a clinician in supporting a patient presenting pulmonary distress. A controller with a touch-screen display operates a positive or negative pressure gas source that communicates with the intubated or negative pressure configured patient through valved supply and exhaust ports. A variety of peripheral, central, and/or supply/exhaust port positioned sensors may be included to measure pressure, volumetric flow rate, gas concentration, transducer, and chest wall breathing work. Innovative modules and routines are incorporated into the controller module enabling hybrid, self-adjusting ventilation protocols and models that are compatible with nearly every conceivable known, contemplated, and prospective technique, and which establish rigorous controls configured to rapidly adapt to even small patient responses with great precision so as to maximize ventilation and recruitment while minimizing risks of injury, atelectasis, and prolonged ventilator days.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 12/131,922 filed Jun. 2, 2008, which claims priority to U.S. Provisional Patent Application No. 60/924,835 filed Jun. 2, 2007. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to the field of ventilating human patients. More particularly, the present invention relates to an improved ventilator and method of operation for ventilation intervention and initiation, oxygenation, recruitment, ventilation, initial weaning, airway pressure release ventilation weaning, continuous positive airway pressure weaning, and continuous and periodic management and control of the ventilator. 
         [0004]    2. Description of Related Art 
         [0005]    The inventor herein has previously invented, among other inventions, ventilator systems and methods of operation disclosed and claimed in U.S. Pat. No. 7,246,618, and in U.S. Patent Application Nos. 2008/0072901, 2006/0174884, 2003/0111078, all of which are incorporated by reference in their entirety as though fully set forth herein. 
         [0006]    Airway pressure release ventilation (APRV) is a mode of ventilation believed to offer advantages as a lung protective ventilator strategy. APRV is a form of continuous positive airway pressure (CPAP) with an intermittent release phase from a preset CPAP level. Similarly, APRV allows maintenance of substantially constant airway pressure to optimize end inspiratory pressure and lung recruitment. The CPAP level optimizes lung recruitment to prevent or limit low volume lung injury. In addition, the CPAP level provides a preset pressure limit to prevent or limit over distension and high volume lung injury. 
         [0007]    The intermittent release from the CPAP level augments alveolar ventilation. Intermittent CPAP release accomplishes ventilation by lowering airway pressure. In contrast, conventional ventilation elevates airway pressure for tidal ventilation. Elevating airway pressure for ventilation increases lung volume towards total lung capacity (TLC), approaching or exceeding an upper inflection point of an airway pressure-volume curve (P-V curve). The P-V curve includes two limbs joined by upper and lower inflection points: an inspiratory or inspiration limb that is opposite an expiratory or expiration limb. Limiting ventilation below the upper inflection of the P-V curve is one the goals of lung protective strategies. 
         [0008]    Subsequently, tidal volume reduction is necessary to limit the potential for over distension. Tidal volume reduction produces alveolar hypoventilation and elevated carbon dioxide levels. Reduced alveolar ventilation from tidal volume reduction has led to a strategy to increase respiratory frequency to avoid the adverse effects of hypercapnia. However, increased respiratory frequency is associated with increase lung injury. In addition, increase in respiratory frequency decreases inspiratory time and lessens the potential for recruitment. Furthermore, increasing respiratory frequency increases frequency dependency and decreases potential to perform ventilation on the expiratory limb of the P-V curve. 
         [0009]    During APRV, ventilation occurs on the expiratory limb of a pressure-volume curve. The resultant expiratory tidal volume decreases lung volume, eliminating the need to elevate end inspiratory pressure above the upper inflection point. Therefore, tidal volume reduction is unnecessary. CPAP levels can be set with the goal of optimizing recruitment without increasing the potential for over distension. Consequently, end inspiratory pressure can be limited despite more complete recruitment, while ventilation can be maintained. 
         [0010]    APRV was developed to provide ventilator support to patients with respiratory failure. Clinical use of APRV is associated with decreased airway pressures, decreased dead space ventilation and lower intra-pulmonary shunting as compared to conventional volume and pressure cycled ventilation. APRV limits excessive distension of lung units, thereby decreasing the potential for ventilator induced lung injury (VILI), a form of lung stress. In addition, APRV reduces minute ventilation requirements, allows spontaneous breathing efforts and improves cardiac output. 
         [0011]    APRV is a form of positive pressure ventilation that augments alveolar ventilation and lowers peak airway pressure. Published data on APRV has documented airway pressure reduction on the order of 30 to 40 percent over conventional volume and pressure cycled ventilation during experimental and clinical studies. Such reduction of airway pressure may reduce the risk of VILI. APRV improves ventilation to perfusion ratio (V/Q) matching and reduces shunt fraction compared to conventional ventilation. Studies performed utilizing multiple inert gas dilution and excretion technique (MIGET) have demonstrated less shunt fraction, and dead space ventilation. Such studies suggest that APRV is associated with more uniform distribution of inspired gas and less dead space ventilation than conventional positive pressure ventilation. 
         [0012]    APRV is associated with reduction or elimination of sedative, inotropic and neuromuscular blocking agents. APRV has also been associated with improved hemodynamics. In a ten year review of APRV, Calzia reported no adverse hemodynamic effects. Several studies have documented improved cardiac output, blood pressure and oxygen delivery. Consideration of APRV as an alternative to pharmacological or fluid therapy in the hemodynamically-compromised, mechanically-ventilated patient has been recommended in several case reports. 
         [0013]    APRV is a spontaneous breathing mode of ventilation that allows unrestricted breathing effort at any time during the ventilator cycle. Spontaneous breathing in Acute Lung Injury/Acute Respiratory Distress Syndrome (ALI/ARDS) has been associated with improved ventilation and perfusion, decreased dead space ventilation and improved cardiac output and oxygen delivery. ALI/ARDS is a pathological condition characterized by marked increase in respiratory elastance and resistance. 
         [0014]    However, most patients with ALI/ARDS exhibit expiratory flow limitations. Expiratory flow limitations results in dynamic hyperinflation and intrinsic positive end expiratory pressure (PEEP) development. In addition, ARDS patients experience increased flow resistance from external ventilator valving and gas flow path circuitry including the endotracheal tube and the external application of PEEP. 
         [0015]    Several mechanisms can induce expiratory flow limitations in ALI/ARDS. In ALI/ARDS both functional reserve capacity (FRC) and expiratory flow reserve are reduced. Pulmonary edema development and superimposed pressure result in increased airway closing volume and trapped volume. In addition, the reduced number of functional lung units (derecruited lung units or alveolar and enhanced airway closure) decrease expiratory flow reserve further. Low volume ventilation promotes small airway closure and gas trapping. In addition elevated levels of PEEP increase expiratory flow resistance. In addition to downstream resistance, maximal expiratory flow depends on lung volume. The elastic recoil pressure stored in the preceding lung inflation determines the rate of passive lung deflation. 
         [0016]    APRV expiratory flow is enhanced by utilization of an open breathing system and use of low (0-5 cm H 2 O) end expiratory pressure. Ventilation on the expiratory limb of the P-V curve allows lower PEEP levels to prevent airway closure. Lower PEEP levels result when PEEP is utilized to prevent derecruitment rather than attempting partial recruitment. Increasing PEEP levels increases expiratory resistance, and conversely lower PEEP levels reduce expiratory resistance, thereby accelerating expiratory flow rates. Sustained inflation results in increased lung recruitment (increased functional lung units and increased recoil pressure) and ventilation along the expiratory limb (reduced PEEP and expiratory flow resistance), improving expiratory flow reserve. 
         [0017]    In addition, release from a sustained high lung volume increases stored energy and recoil potential, further accelerating expiratory flow rates. Unlike low volume ventilation, release from a high lung volume increases airway caliber and reduces downstream resistance. Maintenance of end expiratory lung volume (EELV) to eliminate the inflection point of the flow volume curve and the use of an open system allows reduction in circuitry flow resistance. EELV is maintained by limiting the release time and titrated to the inflection point of the flow time curve. 
         [0018]    Reduced levels of end expiratory pressure are required when ventilation occurs on the expiratory limb of the P-V curve. In ALI/ARDS, increased capillary permeability results in lung edema. Exudation from the intravascular space accumulates, and superimposed pressure on dependent lung regions increases and compresses airspaces. Dependent airspaces collapse and compressive atelectasis results in severe V/Q mismatching and shunting. Regional transpulmonary pressure gradients that exist in the normal lung are exaggerated during the edematous phase of ALI/ARDS. Patients typically being in the supine position, such that forces directed dorsally and cephalad progressively increase pleural pressures in dependent lung regions. Ventilation decreases as pleural pressure surrounding the dependent regions lowers transalveolar pressure differentials. Full ventilatory support during controlled ventilation promotes formation of dependent atelectasis, increase V/Q mismatching and intrapulmonary shunting. Increasing airway pressure can re-establish dependent transpulmonary pressure differential but at the risk of over distension of nondependent lung units. 
         [0019]    Alternatively, spontaneous breathing, as with APRV, can increase dependent transpulmonary pressure differentials without increasing airway pressure. APRV allows unrestricted spontaneous breathing during any phase of the mechanical ventilator cycle. As noted, spontaneous breathing can lower pleural pressure, thereby increasing dependent transpulmonary pressure gradients without additional airway pressure. Increasing dependent transpulmonary pressure gradients improves recruitment and decreases V/Q mismatching and shunt. 
         [0020]    As compared to pressure support ventilation (PSV) multiple inert gas dilution technique, APRV provides spontaneous breathing and improved V/Q matching, intrapulmonary shunting and dead space. In addition, APRV with spontaneous breathing increased cardiac output. However, spontaneous breathing during pressure support ventilation was not associated with improved V/Q matching in the dependent lung units. PSV required significant increases in pressure support levels (airway pressure) to match the same minute ventilation. 
         [0021]    Conventional lung protective strategies are associated with increased use of sedative agents and neuromuscular blocking agents (NMBA). The increased use of sedative and NMBA may increase the time the patient must remain on mechanical ventilation (“vent days”) and increase complications. NMBA are associated with prolonged paralysis and potential for nosocomial pneumonia. APRV is a form of CPAP that allows unrestricted spontaneous breathing. 
         [0022]    Decreased usage of sedation and neuromuscular blocking agents (NMBA) has been reported with APRV. In some institutions, APRV has nearly eliminated the use of NMBA, resulting in a significant reduction in drug costs. In addition to drug cost reduction, elimination of NMBA is thought to reduce the likelihood of associated complications such as prolonged paralysis and may facilitate weaning from mechanical ventilation. 
         [0023]    Mechanical ventilation remains the mainstay management for acute respiratory failure. However, recent studies suggest that mechanical ventilation may produce, sustain or increase the risk of acute lung injury (ALI). Ventilator induced lung injury (VILI) is a form of lung stress failure associated with mechanical ventilation and acute lung injury. Animal data suggest that lung stress failure from VILI may result from high or low volume ventilation. High volume stress failure is a type of stretch injury, resulting from over distension of airspaces. In contrast, shear force stress from repetitive airway closure during the tidal cycle from mechanical ventilation results in low volume lung injury. 
         [0024]    Initially, lung protective strategy focused on low tidal volume ventilation to limit excessive distension and VILI. Amato in 1995 and in 1998 utilized lung protective strategy based on the pressure-volume (P-V) curve of the respiratory system. Low tidal volumes (6 ml/kg) confined ventilation between the upper and lower inflection points of the P-V curve. End expiratory lung volume was maintained by setting PEEP levels to 2 cm H 2 O above the lower inflection point. Amato demonstrated improved survival and increased ventilator free days. 
         [0025]    However, subsequent studies by Stewart and Brower were unable to demonstrate improved survival or ventilator free days utilizing low tidal volume ventilation strategy. Unlike Stewart and Brower, Amato utilized elevated end expiratory pressure in addition to tidal volume reduction. Such important differences between these studies limited conclusions as to the effectiveness of low tidal ventilation limiting ventilator associated lung injury (VALI). 
         [0026]    Recent completion of the large controlled randomized ARDSNet trial documented improved survival and ventilator free days utilizing low tidal volume ventilation (6 ml/kg) vs. traditional tidal volume ventilation (12 ml/kg). Although the low tidal volume group (6 ml/kg) and traditional tidal volume group (12 ml/kg) utilized identical PEEP/FiO 2  scales, PEEP levels were significantly higher in the low tidal volume group. Higher PEEP levels were required in the low tidal volume group in order to meet oxygenation goals of the study. Despite improved survival in the low tidal volume group (6 ml/kg) over traditional tidal volume group (12 ml/kg), survival was higher in the Amato study. The ARDSNet trial also failed to demonstrate any difference in the incidence of barotrauma. The higher PEEP requirements and the potential for significant intrinsic PEEP from higher respiratory frequency in the lower tidal volume group, may have obscured potential contribution of elevated end expiratory pressure on survival. Further studies are contemplated to address the issue of elevated end expiratory pressure. 
         [0027]    In the prior art, utilization of the quasi-static inspiratory pressure versus volume (P-V) curve has been advocated as the basis or controlling a ventilator to carry out mechanical ventilation. The shape of the inspiratory P-V curve is sigmoidal and is described as having three segments. The curve forms an upward concavity at low inflation pressure and a downward concavity at higher inflation pressures. Between the lower concavity and the upper concavity is the “linear” portion of the curve. The pressure point resulting in rapid transition to the linear portion of the curve has been termed the “lower inflection point”. 
         [0028]    The lower inflection point is thought to represent recruitment of atelectatic alveolar units. The increasing slope of the P-V curve above lower inflection point reflects alveolar compliance. Above the inflection point, the majority of air spaces are opened or “recruited”. Utilizing the lower inflection point of the inspiratory P-V curve plus 2 cm H 2 O has been proposed to optimize alveolar recruitment. Optimizing lung recruitment prevents tidal recruitment/derecruitment and cyclic airway closure at end expiration. Ultimately, optimizing lung recruitment could potentially reduce shear force generation and low volume lung injury. 
         [0029]    Despite an increase in the knowledge of those skilled in the relevant arts as to how to improve and maintain recruitment which minimizes the possibility of VILI and other anomalies, the systems, devices, and methods of the prior remain difficult to operate and employ for use with the best practice protocols. While due to many constraints, the often-cited challenges complained of by those skilled and practicing in the intensive care respiratory technical field is that a more automated and more accurate means is needed for applying the best practice APRV techniques. 
         [0030]    More specifically, what has long been needed are improved devices and modes of operation that enable a clinician to more readily configure and reconfigure the desired APRV approach to respond to the individual presentation of each patient. Preferably, such improved APRV devices and methods for use would establish the capability to give the clinical practitioner a comprehensive starting point of suitable APRV parameters that could be quickly fine-tuned to meet the needs of a particular patient. 
         [0031]    More preferably, such an improved method and ventilator device would also be able to capture the real-time patient condition information used by a clinician in monitoring patient response to the initial APRV parameters, and to generate a more automated feedback loop that would enable the improved method or device to be automatically reconfigured within clinically preferred operational and protocol constraints. Even more preferably, a new method and apparatus is needed that would also enable more accurate and smaller adjustments to the various APRV parameters that is presently possible with the present day equipment and methods, which must be manually adjusted. Such manual adjustments often result in unfavorable patient response that results from inaccurate adjustments or adjustments that cannot be made with enough precision due to the constraints or limited capabilities of the presently available equipment. 
         [0032]    Most preferably, what is needed is a new and improved ventilator that incorporates new features and a mode of operation enabling greater flexibility, higher accuracy, and faster clinical response times in making adjustments to the various P-V curve and related parameters to accommodate unexpectedly changing patient conditions. 
       SUMMARY OF THE INVENTION 
       [0033]    Many heretofore unmet needs are met and problems of the prior art are solved with the innovative ventilator embodiments according to the principles of the invention. Such features and capabilities may preferably or optionally include, among other elements and for purposes of illustration and example but not for purposes of limitation, improved and more accurate ventilation capabilities than has been possible with the many prior attempts. 
         [0034]    In one preferred configuration of the invention, a ventilator or ventilator system for assisting the respiratory function of a patient under the direction of a clinician contemplates the ventilator having a computerized, operation controller or control module or computing device that is in electronic communication with an intra-ventilator and/or extra-ventilator electrical or data circuit or data network. The controller also preferably includes a display, which can be a touch-screen display or any other suitable display, including an application-specific, customized display that incorporates data input or receiving devices into the display, with or without a touch-screen capability. 
         [0035]    The controller or computing device also preferably includes a memory or storage capability that can include hard disk drives, removable drives and any desired form of storage device. Input devices are also desirable and can include keyboards, mouse pointers, data entry tablets, voice-activated input devices, and electronic media reading devices, among many others. 
         [0036]    Additionally contemplated input devices include wired and wireless communications components for networking, data transfer, data capture, and data monitoring such as monitoring communications from electro-impedance tomography devices, ultrasound equipment, computed and computer-aided tomography devices, digital output fluoroscopes, x-ray equipment, magnetic resonance imaging and spectroscopy equipment, minimally invasive surgical and bronchoscopic visualization devices, and similarly capable equipment. 
         [0037]    The inventive ventilators of the invention also preferably include a gas supply pump and/or pressurized gas source. The gas pump or source supplies positive pressure gas to the patient through a gas circuit or network of pipes, tubes, hoses, or other types of conduits. The gas network or circuit may also include at least one and more preferably a plurality of valves and supply and exhaust ports. More preferably, a number of valves may be incorporated that can be electronically in communication with the controller or computing device for actuation. 
         [0038]    Such valves can typically be included in line with the supply and exhaust ports and can be operable in cooperation with the various types of sensors discussed elsewhere herein. What are often referred to as back-check valves, which enable fluid flow in one direction but which prevent fluid flow in an opposite direction. Such check valves may be included in the gas circuit or network to protect various components and the patient from unexpected and/or undesirable pressures or pressure shock. In this way, protection can be afforded to the patient, pump or pressurized gas source, sensors, and other equipment. 
         [0039]    Other preferably optional embodiments of the invention are directed to ventilation and control in negative pressure applications and the contemplated gas supply pump or pressurized gas source also may preferably incorporate, either alone or in combination with any of the other features described elsewhere herein, a negative pressure or vacuum capability that is contemplated to be compatible for use with negative pressure thoracic or full-body cylinders, which are also sometimes referred to by those skilled in the ventilation and respiratory technical fields as single, biphasic, or multiphasic iron-lung or cuirass ventilators. 
         [0040]    More preferably, the ventilators practiced according to the invention also preferably include any number of optional detectors, sensors, or detection devices, that can be used alone or in any combination to sample and determine pressures of the supplied gas, inspired gas, expired gas, at rest, inflection point, and many different types of dynamic patient airway pressures. Other useful sensors can include peripheral, central, and airway gas concentration sensors that can be positioned extracorporeally in the case of well-known capnometers (for detecting carbon-dioxide concentrations) or infrared oximeters (for detecting oxygen concentrations). 
         [0041]    These types of devices can be attached to extremities such as fingers, toes, or ear lobes, which make it very convenient to sample, monitor, and detect peripheral concentrations or saturations of carbon dioxide (SpCO 2 ) and oxygen (SpO 2 ). For other contemplated ventilation applications, central line catheters or other techniques can enable monitoring of arterial O 2  and CO 2  gas concentrations (PaO 2 ,PaCO 2 ), which can have clinical value in certain ventilation modes of operation or protocols discussed elsewhere herein. For purposes of the instant invention, such pressure and gas concentration sensors are more preferably configured to electronically communicate with the contemplated controller or computing device of the ventilator so that the real-time and/or near-real-time data can be monitored as described in more detail below. 
         [0042]    The inventive ventilator also contemplates incorporation of any number of equally suitable fluid flow rate sensors that also may be adapted to communicate with the data network, the data circuits, and/or directly with the controller or control module or computing device, and either wirelessly or over wired connections. Such flow rate monitoring devices can be employed in multiple places in the gas network or circuit to monitor the total amount of gas supplied, inspired, expired, as well as the speed at which such activity is occurring or has occurred. With this information, pressure can be compared to total volume or rate of volumetric or mass flow of gas so that the novel ventilators can better control and ensure proper ventilation of the target respiratory system of the patient. 
         [0043]    Additionally, such controls can improve the accuracy with which pressurized gas is supplied to the patient, and can lessen the risk of lung injury by monitoring and keeping gas flow rates within acceptable protocol limits. In any number of possible preferred configurations, the sensors can be arranged as a sensor array to simultaneously monitor any one or any number of ventilation-related parameters so as to maximize control over the ventilation procedure to ensure the best possible protocol implementation under the circumstances. In many preferably optional configurations of the invention, any of the noted sensors may be positioned proximate to and/or about the gas supply and/or exhaust ports, among other places in the gas network or circuit. 
         [0044]    A command module, command routine, algorithm, commander, firmware, or program may preferably be resident in the memory or storage components of the controller or computing device. The command module is preferably operative to control the sensors, to control the supply pump, to receive communications or images or information from other devices, to receive input from the clinician or another via any of the contemplated input devices, and to operate the display to present prompts and/or display important information pertaining to the ventilation process. The command module may also be optionally configured to preferably communicate various ventilator information to other devices, to other wireless or wired networks, to the display for contemporaneous viewing, and to other remote devices and locations as may be desired. 
         [0045]    Preferably, the control module may adjustably and/or variably actuate the pump or pressure source to vary the volume and/or pressure supplied thereby. Further, the control module or command routine may more preferably be modified to also automatically, manually, or otherwise operate any of the plurality of valves, either alone or in combination with the control of the pump, for even more rigorous control over the pressure, volume, flow rate, and gas supply cycle times available for use in ventilating the patient. More preferably, the control module or command routine may preferably be adapted to coordinate such control of the valves with sampling of or receipt of information from any of the contemplated sensors to establish increased accuracy in sampling one or more pressure readings, gas concentrations, and/or volume or mass flow rates anywhere in the gas circuit or network, or the patient undergoing ventilation. 
         [0046]    The present invention also contemplates operational compatibility with any number of conventionally accepted, investigational, and experimental ventilation modes. More preferably, the operational capability of the invention enables many heretofore unavailable hybrid modes wherein the innovative ventilator automatically changes its mode of operation in response to patient progress or difficulties. For example, the ventilator can be configured to commence ventilation in a mandatory breath mode, and to monitor various patient pressure, volumetric, and gas concentration responses, among other responses, that may indicate a patient who was formerly heavily sedated and unable to breathe, has suddenly started to attempt to breathe spontaneously. 
         [0047]    Upon such detection, the inventive ventilation will automatically switch among many modes of operation including from full-support mandatory breath modes, to various modes having lesser degrees of breathing support, so as to cooperate with the patient&#39;s attempts to breathe independently. Additionally, if the patient relapses and discontinues spontaneous breathing attempts, the ventilator will revert to full, mandatory breath mode. To enable such capabilities, the new ventilator of the invention is preferably preconfigured with various automated and reconfigurable modes of operation. For purposes of assisting clinicians with selecting fully automated modes of operation, or to enable partial or fully customizable modes of operation, the optionally preferred configurations of the invention enable the clinician to select any particularly desired automated mode of operation. 
         [0048]    Additionally, the clinician may also select an automated mode of operation and then modify only the desired parameters. Even further, the clinician may ignore the fully automated modes, and may enter preferred settings to select a fully customized mode of operation suitable for purposes of any conceivable ventilation protocol or mode of operation. In one particularly useful configuration, the ventilator incorporates the controller or control module or computing device to have three primary operational modules, including, for purposes of example but not for purposes of limitation, an initial setup module, an adjustment and maintenance module, and a weaning module. 
         [0049]    In turn, the initial setup module includes among other elements, an optimal end expiratory lung volume (OEELV) sub-module that monitors a number of key patient parameters to ascertain and periodically compute the OEELV. The adjustment and maintenance module includes oxygenation, recruitment, and ventilation sub-modules of operation and protocols that are tightly constrained to rigorously and aggressively monitor and protect the key aspects of these ventilation operational modes. This is accomplished using precisely bounded monitoring paradigms that enable very gradual and extremely accurate changes to manage CO 2  ventilation, to ensure optimal oxygen saturation, and, when needed, to exercise and maximize alveolar recruitment and prevent derecruitment. If any parameters experience unexpected or uncontrolled hysteresis, alarm events are triggered to enable intervention. 
         [0050]    The weaning module includes an initial weaning assessment sub-module that enables close monitoring and small, slow changes to assess patient response to reduced ventilator support with rapid fall back to full support as needed. With positive patient response, the initial weaning assessment sub-module enables complete ventilator reconfiguration into subsequently less supportive ventilation protocols for further weaning. Also included in the weaning module is an airway pressure release ventilation or APRV sub-module wherein spontaneous patient breaths are closely monitored so that support can be weaned as the patient gains control and consistency. With continued improvement, control is passed to the CPAP sub-module, which cycles up to a maximum CPAP support mode that is then gradually reduced to a minimal support mode until an extubation pressure is reached, at which point the patient is completely weaned from the ventilator. 
         [0051]    For purposes of achieving these various modes of use, any of preferred or optional variations of the inventive ventilator may be predefined with or may receive and capture a number of parameters that can control how the ventilator operates in its various modes of operation. The controller or computing device may access stored parameters, may obtain new parameters from remote devices via wired or wireless communications, and may accept user input via the noted touch-screen display or any of the other input devices. Whatever the source of the operational settings or parameter, the information is typically stored in a database or an array that is stored in the memory or storage of the controller or computing device. In one optionally preferred embodiment, these parameters are accessibly stored in one or more initialization parameter database(s), which may be resident in the controller memory or storage. 
         [0052]    These initialization parameters can be accessed and displayed or communicated to any other device. Alone or in combination with this database, additional subsets of parameters may be grouped together in arrays such as one or more model patient data arrays or elements, which can be predefined to represent optimum ventilator settings that are well suited for a particular type of presenting patient or disease. 
         [0053]    For purposes of illustration, but not for purposes of limitation, such data arrays or initialization parameter databases may include, among other parameters and information, a PEEP, a target peripheral O 2  concentration or an SpO 2  quantity, an end tidal CO 2  or etCO 2  quantity, a fraction of inspired O 2  or FiO 2  quantity, a high pressure or P(high) that defines the maximum inspired pressure during mandatory or positive pressure assisted breaths, a low pressure or P(low) that can define a minimum pressure to be used during expiration and which can be zero or non-zero. Other parameters can include a high time or T(high) that represents a period of inspiration during P(high) and a low time or T(low) that can represent a small period of time during which expiratory gas is expelled. 
         [0054]    It may also be optionally preferred to include predefined or predetermined pressure change increments or pressure increments, P(inc), and time increments, T(inc), which can be any amount, and for which there can be multiple different preset increments that can be used as needed and so that clinical intervention may not be needed in more automated modes of operation. It has also been found to be sometimes desirable to store one or more tidal volumes, respiratory frequencies for mandatory breaths, to establish and store one or more pressure-volume curve slopes, and to establish one or more trigger pressures that enable the ventilator to detect a pressure drop trigger, which may indicate the patient is trying to spontaneously breathe. 
         [0055]    In yet further optionally preferred variations, the ventilator may also be configured so that the command module can receive such initialization settings from the user or the clinician via the input device. Such settings can include those described elsewhere herein or any other possibly desirable parameters that can improve the use of the ventilator. Once any preferred settings and/or parameters are entered into the controller and/or command routine, the supply pump is actuated to begin ventilation within the constraints of the selected automated program or settings or the manually entered parameters and settings. 
         [0056]    During operation, the command module or routine samples, polls, or otherwise communicates with, any or all of the sensors in the array and measures the patient&#39;s actual data. A series of such sensor readings may be sampled so that an entire array of such data elements can be used to monitor patient response and ventilator performance, and to adapt the ventilator performance in response to patient status and condition. For purposes of example without limitation, sensor data that can be gathered may optionally include a patient SpO 2  partial pressure (PP) or quantity, a patient etCO 2  PP or quantity, a peak expiratory flow rate (PEFR), an end expiratory lung volume (EELV) and a spontaneous frequency or machine respiratory frequency. 
         [0057]    Once measured or sampled, the actual patient data array elements can be compared by the command module to any of the stored data to ascertain ventilator performance and patient response. For further example, such actual data may be compared to the one model patient data array. In this way, it can be determined whether the patient is responding favorably to ventilation. In another example, if the patient is responding well to ventilation, then a comparison between the patient&#39;s SpO 2  and etCO 2  and a comparable model patient data set would be acceptable. If acceptable, then the control routine can compute or generate a flag or Boolean value such as an SpO 2  goal value and an etCO 2  goal value that can be set to true, meaning the actual patient measurements indicate all is well. If not, then a false flag can be generated to enable the control routine to modify its behavior or seek clinical intervention by generating an alarm condition. Additionally, the control routine can poll pressure sensors and flow sensors during certain points in the inspiration and expiration phases of ventilation to ascertain an OEELV, which can provide clinically relevant feedback identifying patient response and ventilator performance. 
         [0058]    In yet other optionally preferred configurations, the ventilator may be configured to modify its behavior in response to unfavorable patient response. For further example, assume the SpO 2  was unfavorable and the SpO 2  goal value is false, which indicates undesirable oxygenation. As discussed in more detail elsewhere herein, the command module can preferably determine that increased or modified adjustments in ventilation are warranted to achieve the desired SpO 2  level. To that end, the command module will adjust the operation of the pump, and functioning of the valves, and perhaps the concentration of supplied oxygen in the pressurized gas supply, and may thereby increase the P(high) the pressure increment, it may increase the T(high) by the time increment. In the alternative, it may be instead preferable to only modify the various operational parameters of the ventilator to increase or decrease the FiO 2  quantity. 
         [0059]    More preferably, in circumstances where the patient is responding well and it is warranted to start gently weaning from the ventilator support, the command module can instead set a flag or Boolean constant, such as an initial weaning value to be true, which can serve to notify other modules of the ventilator that weaning may begin. Conversely, if the patient is experiencing difficulties that may include non-perfused pulmonary dead space, it may be advantageous to modify the ventilator behavior to encourage recruitment of alveolar tissues. In certain circumstances, it may be advisable to generate an alarm signal seeking intervention. In other less challenging circumstances, it may desirable to set a recruitment flag or Boolean value to notify other control routine modules that a recruitment process is advisable. In this circumstance, the control routine can modify the pump and valve operation to establish operation suitable for recruitment, which can include increasing P(high) by one or more P(inc), increasing T(high) by one or more T(inc)s, and/or adjusting T(low) by one or more T(inc)s. 
         [0060]    In other situations where recruitment may not be indicated, it may be desirable to increase lung oxygenation. If so, the controller or computing device may make adjustments to the ventilator operation whereby an oxygenation flag or Boolean value is set to be true, which can invoke an oxygenation module that can poll the sensors to measure the peak expiratory flow rate and then compute an angle of deceleration of gas flow so that an appropriate time adjustment may be made, or so that T(low) may be decreased by one or more T(inc). 
         [0061]    In yet other equally useful modes of operation, the ventilator can invoke an alveolar ventilation approach wherein the command module compares the spontaneous frequency to the machine respiratory frequency, ascertains the P(high), T(high), computes a minute ventilation (MV) value, adjusts the supply pump and valves to increase T(high) and P(high) by respective T(inc) and P(inc). Similarly, a minute ventilation and recruitment module may be invoked wherein the MV is computed as a function of the currently in use P(high) and T(high), and adjustments are made to the P(high) and T(high). 
         [0062]    In more favorable patient response scenarios, an initial weaning assessment sub-module may be utilized wherein the command module or command routine samples the machine respiratory frequency and spontaneous respiratory frequency to ascertain that spontaneous breathing is occurring at a certain rate. Comparing this rate to a predefined rate gives a good indication of whether an initial weaning assessment sub-module can be employed. If so, then the command routine can test for apnea and tachypnea. If neither condition is indicated, then the ventilator can be switched to a more suitable mode, such as an APRV mode, which makes it much easier for the intubated patient to breathe spontaneously. 
         [0063]    As the patient who is experiencing initial ventilator weaning continues to improve, another mode of the ventilator enables a weaning module wherein spontaneous breathing and blood gas levels continue to be monitored while the P(high) is decreased while the T(high) is increased. In this way, the patient is encouraged to continue spontaneous breaths. 
         [0064]    As improvements mount, further weaning is warranted. In this instance, the ventilator operates in another mode wherein weaning criteria can be considered in comparison to the actual patient data that is being monitored. In one suitable set of predetermined weaning criteria, an FiO 2  threshold, an SpO 2  threshold, a spontaneous tidal volume, a minute ventilation quantity, and an airway occlusion pressure (P0.1) are compared to the patient&#39;s actual values. If the patient fails to meet these criteria, then weaning is discontinued temporarily and more breathing support is given to the patient. In weaning failure, the control routine increases the P(high) and decreases T(high). Conversely, if the weaning criteria are passed by the patient&#39;s actual values, then the command module repeatedly initiates the cyclic weaning protocol wherein P(high) is decreased and T(high) is increased. The airway occlusion pressure P0.1 is measured and trended over time by a P0.1 module and is used to assess the work of breathing during spontaneous breaths. In the preferred embodiments, this is used to assess the impact of weaning and the resultant work of breathing, as is explained in connection with other modules elsewhere herein. 
         [0065]    Assuming for further purposes of illustration that the patient continues improving, then the command module changes ventilator operation again, and monitors P(high) until a CPAP threshold is reached, which enables another conversion of the ventilator operation into a CPAP sub-module. This sub-module is much more comfortable for patients, and reduces the dependence of the ventilator. As the further improvements are manifested, the command module begins to gradually reduce the CPAP pressure until an extubation threshold pressure is reached. Also, it may be optionally preferable during the CPAP and other modes of operation to enable the controller to incorporate an automatic tube compensation pressure or ATC pressure which boosts the ventilator support just enough to overcome the frictional losses encountered when breathing through the gas network or circuit of tubing involved in use of the ventilator. 
         [0066]    In operation, various methods of use of the ventilator are possible using any of the embodiments of the invention and modifications, variations, and alternative arrangements thereof. Using any of the physical configurations of the inventive ventilators described elsewhere herein, one method of use involves entering settings via the input device including at least one of (i) an automated initialization setting and (ii) a parameter to be stored in the memory that includes at least one of (a) a PEEP quantity, (b) an SpO 2  quantity, (c) an etCO 2  quantity, (d) an FiO 2  quantity, (e) a high pressure, (f) a low pressure, (g) a high time, (h) a low time, (i) a pressure increment, (j) a time increment, (k) a tidal volume, (l) a respiratory frequency, (m) a pressure-volume slope, (n) a trigger pressure, and (o) a predetermined weaning criteria including at least one of an FiO 2  threshold, an SpO 2  threshold, a spontaneous tidal volume, a minute ventilation quantity, and an airway occlusion pressure (P0.1). 
         [0067]    Next, the command routine receives the settings from the clinician via the input device and commands the controller to actuate the supply pump. This commences respiratory assistance to the patient whereby the gas circuit communicates with the patient using one each of the FiO 2  quantity, the high and low pressure, and the high and low time. Patient actual data array elements are measured by using the command routine to communicate with the plurality of sensors. Measurement of at least one of (i) a patient SpO 2  quantity, (ii) a patient etCO 2  quantity, (iii) a peak expiratory flow rate, (iv) an end expiratory lung volume and (v) a spontaneous frequency, is taken. 
         [0068]    The command routine compares the patient actual data array to at least one of the settings and computes at least one of an SpO 2  goal value, an etCO 2  goal value, and an optimal end expiratory lung volume, which values are used to determine whether the patient should be initially weaned, undergo recruitment and increased oxygenation, or be maintained in an unaltered state of ventilation. 
         [0069]    If the patient is improving, then measuring and comparing at least one of the patient actual data array elements to the predetermined weaning criteria to set a flag or Boolean weaning value to true is warranted (meaning the patient did not fail the weaning test). If passed, the cyclic weaning is initiated by adjusting at least one of the supply pump and the plurality of valves to decrease the P(high) by one or more pressure increments. 
         [0070]    Also, to decrease the ventilator support even further, the T(high) is gradually increased and the P(high) is gradually decreased until the CPAP threshold is reached, where after the ventilator is switched into CPAP mode where it remains until the CPAP pressure may be decreased until the extubation threshold pressure is reached, after which the patient may be removed from the ventilator. 
         [0071]    In other optionally preferred novel embodiments, any of the monitoring devices, sensors, computers, or computing devices may be connected with any of the other components wirelessly or with a wire. Any of the contemplated components may also be in communication with any of the other components across a network, through a phone line, a power line, conductor, or cable, and/or over the internet. In other alternatively preferred configurations of the invention, the resident software program may have numerous features that, for purposes of example without limitation, enable different functionalities. 
         [0072]    More preferably, such resident software program and/or programs may enable any of the contemplated information to be communicated by text, voice, fax, and/or email messages either periodically, when certain predefined or predetermined conditions occur, such as predefined alarm events or conditions, and/or when anomalous, unexpected, or expected power readings occur and/or are detected. 
         [0073]    These variations, modifications, and alterations of the various preferred and optional embodiments may be used either alone or in combination with one another and with the features and elements already known in the prior art and also herein contemplated and described, which can be better understood by those with relevant skills in the art by reference to the following detailed description of the preferred embodiments and the accompanying figures and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING(S) 
         [0074]    Without limiting the scope of the present invention as claimed below, and referring now to the drawings and figures, wherein like reference numerals across the drawings, figures, and views refer to identical, corresponding, or equivalent elements, methods, components, features, and systems: 
           [0075]      FIG. 1  shows a ventilator and system in accordance with the present invention; 
           [0076]      FIG. 2  shows a schematic diagram of the operation of the ventilator and system of  FIG. 1 ; 
           [0077]      FIGS. 3   a  and  3   b  are schematic diagrams of an OEELV sub-module of operation of the ventilator and system of  FIG. 1 ; 
           [0078]      FIG. 4  shows a schematic diagram of the interrelationships between the modules of operation of the ventilator and system of  FIG. 1 ; 
           [0079]      FIG. 5  shows a schematic diagram of an oxygenation sub-module of operation of the ventilator and system of  FIG. 1 ; 
           [0080]      FIG. 6  is a schematic diagram of a recruitment sub-module of operation of the ventilator and system of  FIG. 1 ; 
           [0081]      FIG. 7  is a schematic diagram of a ventilation sub-module of operation of the ventilator and system of  FIG. 1 ; 
           [0082]      FIG. 8  is schematic diagram of an initial weaning assessment sub-module of operation of the ventilator and system of  FIG. 1 ; 
           [0083]      FIG. 9  is schematic diagram of an ARPV sub-module of operation of the ventilator and system of  FIG. 1 ; 
           [0084]      FIG. 10  is a schematic diagram of a CPAP sub-module of operation of the ventilator and system of  FIG. 1 ; 
           [0085]      FIG. 11  is an area diagram of an OEELV sub-module and assessment of operation of the ventilator and system of  FIG. 1 ; 
           [0086]      FIG. 12  is an area diagram of an OEILV sub-module and assessment of operation of the ventilator and system of  FIG. 1 ; 
           [0087]      FIG. 13  is an area diagram of a spontaneous breathing sub-module and assessment of operation of the ventilator and system of  FIG. 1 ; 
           [0088]      FIG. 14  is a schematic airway pressure versus time tracing for airway pressure release ventilation; 
           [0089]      FIG. 15  is an airway pressure versus time tracing during the inspiratory P(high) phase of ventilation; 
           [0090]      FIG. 16  is an airway volume versus pressure curve illustrating a shift from the inspiratory limb to the expiratory limb thereof; 
           [0091]      FIG. 17  is an inspiratory and expiratory gas flow versus time tracing for airway pressure release ventilation; 
           [0092]      FIG. 18  is an expiratory gas flow versus time tracing; 
           [0093]      FIG. 19  is a set of expiratory gas flow versus time tracing illustrating determination of whether flow pattern is normal, restrictive or obstructive based on the shape of the tracing; and 
           [0094]      FIG. 20  is a set of airway pressure versus time tracings illustrating ventilation weaning by successive reductions in pressure P(high) and substantially contemporaneous increases in time T(high). 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0095]    Referring now to the various figures and illustrations, those skilled in the relevant arts should appreciate that each of the preferred, optional, modified, and alternative embodiments of the inventive ventilator and ventilator system  10  and method of operation contemplate interchangeability with all of the various features, components, modifications, and variations within the scope of knowledge of those skilled in the relevant fields of technology and illustrated throughout the written description, claims, and pictorial illustrations herein. 
         [0096]    With this guiding concept in mind, and with reference now to  FIG. 1 , one possible embodiment of a ventilator and ventilator system  10  is illustrated, which is in communication with the patient P undergoing ventilation therapy. The ventilator and ventilator system  10  also preferably includes a gas supply pump and/or pressurized gas source  12  having a positive pressure port  14 , and optionally a negative pressure port  16 . The gas pump or source  12  supplies positive pressure gas  14  and can also supply negative pressure or a vacuum  16  for non-invasive negative pressure applications such as iron-lung or similar therapies. A wide variety of commercially available ventilators may be modified according to the principles of the invention and one such device includes what is referred as the model EvitaXL, which is available from Draeger Medical, Inc. of Telford, Pa., USA, and Lubeck, Germany. 
         [0097]    The ventilator  10  also preferably includes a controller or control module or computing device  20  that is in electronic communication with an intra-ventilator and/or extra-ventilator electrical or data circuit or data network  22 . The controller  20  also preferably includes a display  26 . The display  26  may be a conventional device that receives unidirectional signals from the controller  20 , but may also be any of a number of possibly preferred bidirectional devices such as a touch-screen display that can be used as an input device  28 , and which may also have a data entry capability such as a built-in keyboard or keypad similar to the keyboard input device  28  shown in  FIG. 1 . 
         [0098]    The controller or computing device  20  also preferably includes a memory or storage capability  24  that can include flash drives, optical media, hard disk drives, solid state disk drives, random access memory, non-volatile memory, removable storage devices, remote internet-based storage devices, network appliance-type devices, and the like. 
         [0099]    Typically, the gas supply pump or pressurized gas source  12  communicates positive or negative pressure to the patient P through a gas circuit or network of tubes  40 . The gas network or circuit  40  may also include an inspiration or supply port  42  and an expiratory or exhaust port  44 . A number of valves are usually also included to control and meter fluid flow and would preferably include a supply valve  46 , a sensor valve (not shown), and an exhaust valve  52 , all of which would likely be in communication with the controller  20  via the data network  22  so that the command module  30  may control and operate the valves automatically to start and stop ventilation and to control pressure and flows rates to the patient P during operation. 
         [0100]    The supply and exhaust valves  46  and  52  may be also operable to periodically close for short periods of time to enable pressure sensors to obtain various static pressure readings. Additionally, the sensor valve may be operable to close such as to protect various sensors from pressure circuit transients and to prevent spurious readings such as when the ventilator  10  may be automatically responding to patient P improvements or relapses by changing modes of operation from mandatory breathing support to augmentative support modes. 
         [0101]    In addition to the contemplated input devices described elsewhere herein, there may be certain diagnostic imaging devices that can be incorporated into the operation of the ventilator  10  of the invention to communicate quantitative pulmonary function information such lung volume, dead space ratios, and the like. Additional and possible useful devices may also include, for purposes of example without limitation, electro-impedance tomography devices  70 , ultrasound equipment  80 , computed and computer-aided tomography devices  90 , and other types of Doppler imaging sensors  95  that may enable various quantitative or subjective pulmonary function imagery. 
         [0102]    Various types of optionally preferred detectors, sensors, or detection devices, also have utility for purposes of the invention to enable precise control and analysis of volumetric and mass flow rates as well as pressures of the supplied gas, inspired gas, and expired gas, which in turn enables calculation of various other static and dynamic pulmonary function parameters, as is discussed in more detail elsewhere herein. 
         [0103]    With continued reference to  FIG. 1 , a group of sensors  54  can be arrayed proximate to the ventilator  10  and patient P. An oximeter or O 2  saturation sensor  56  may be used peripherally to ascertain peripheral or venous O 2  content SpO 2  and a capnography sensor or capnometer or CO 2  sensor  58  may be used to determine end tidal or peripheral CO 2  saturation levels (etCO 2 , SpCO 2 ). For certain applications involving long term supine ventilation, it may be desired to also monitor arterial blood gas concentrations, among other parameters. In these instances, invasive methods can be used such as central line catheters to assess pulmonary arterial O 2  and CO 2  levels using a PaO 2  sensor  60  and/or a PaCO 2  sensor  62 . 
         [0104]    It is also optionally preferred to monitor various airway pressures, volumetric, and mass flow rates so that patient P response can be continuously assessed. For purposes of monitoring airway pressures, an airway pressure sensor or pressure gauge  64  can be placed in a number of places along the gas network or circuit, and is more preferably positioned proximate to the supply and exhaust ports  42 ,  44  at the intubation site of the patient P. An airway flow sensor  66  can be similarly positioned to enable monitoring of volumetric flow rates of inspiratory and expiratory gases. In certain applications, it has been found desirable to employ strain gauges mounted on the thorax to enable monitoring of chest movement during pulmonary breathing cycles, which can be an additional source of volumetric pulmonary patient P function as well as a source of patient P work expended for spontaneous breaths. 
         [0105]    With reference now also to  FIG. 2 , the ventilator  10  also incorporates the control module  20  and/or the command module  30  to include three primary operational modules, including, for purposes of example but not for purposes of limitation, an initial setup module or protocol  100 , an adjustment and maintenance module  200 , and a weaning module  250 . During initial ventilator  10  startup, a number of initial parameters are set based upon input from the clinician or by accessing a predefined set of parameters. With reference now also to  FIGS. 2 ,  3 , and  4 , the preliminary initialization routines will be described. In  FIG. 4 , it can be seen that the clinician may enter their preferred settings  110  into the display  26  or input device  28 . In the alternative, any number of possible predefined automated settings  120  may be accessed and used as defined or customized in whole or in part to prepare the ventilator  10  for operation. Once the clinician or automated settings  110 ,  120  are selected, the settings  110 ,  120  are populated with various other initialization parameters  130  during the operation of the initial setup module  100 . As the operation of the ventilator  10  commences, the command module  30  invokes an OEELV sub-module or assessment routine  150 . 
         [0106]    With specific reference now to  FIGS. 3   a  and  3   b , it can be seen that the initial setup module  100  includes the OEELV sub-module or assessment routine  150 . The OEELV sub-module  150  periodically and on demand will determine a ventilation range as a function of obstructiveness of the lung and the hypocarbic, normal, and/or hypercarbic condition of the patient P. As part of the evaluation, the OEELV sub-module  150  determines whether the computationally ascertained OEELV is in the range appropriate for the conditional status of the patient P. For example without limitation, if the patient P has obstructive lungs, and is experiencing high range hypoventilation, i.e., hypercarbia, then an appropriate or desired OEELV should be in the range of about 30% to 40%. 
         [0107]    If the computationally ascertained OEELV is higher than this range, then the T(low) parameter is increased by 0.05 seconds. Conversely, if the computationally ascertained OEELV is lower than the desirable range of 30% to 40%, then the T(low) parameter is lowered with the intent to achieve the appropriate OEELV range. In this way, the novel OEELV sub-module  150  can execute very fine adjustments of actual OEELV to stimulate optimum conditioning of the ventilated patient&#39;s P pulmonary response. To wit, adjustments of 0.05 seconds in T(low) will enable slow and gradual optimization of the OEELV best suited to the disease modality. Although for purposes of illustration and explication of various aspects of the invention, increments of 0.05 seconds or other amounts of time have been described. However, the principles of the invention in this aspect are also suitable for even more gradual changes in time, and can include milliseconds and smaller and larger orders of magnitude. 
         [0108]    Once T(low) is set, the OEELV sub-module  150  relinquishes control for a period of time and the command module  30  again resumes control to then invoke the adjustment and maintenance module  200 , which includes an oxygenation sub-module  300 , a recruitment sub-module  400 , and a ventilation sub-module  500 . The module  200  and its component sub-modules  300 ,  400 , and  500  include protocols configured to rigorously monitor and protect the key aspects of the patient&#39;s P physiological ventilation and pulmonary response profile to enable maximized recovery and weaning with minimum pulmonary injury risk. During the ensuing ventilation process, the patient&#39;s P SpO 2  and etCO 2  are continuously monitored via the respective SpO 2  and etCO 2  sensors  56 ,  58  to ensure a target or goal of SpO 2  of at least about 95% and etCO 2  of no more than between about 34 to 45 mm Hg are maintained ( FIG. 4 ). 
         [0109]    The command module  30  next passes control to oxygenation sub-module  300 , which is described in more detail specifically in  FIGS. 4 and 5 . As the oxygenation sub-module  300  assumes control for a short period of time, the SpO 2  is again assessed so that adjustments may be made as required in the fractionally inspired O 2 , which is otherwise referred to as the FiO 2  parameter  360 . Once adjustments are made to FiO 2    320 ,  340 ,  350 , the command module  30  cooperates with the oxygenation sub-module  300  to assess whether a P(high) pressure adjustment must be made or whether the initial weaning assessment sub-module  600  is invoked. If the patient P is responding well, and if the FiO 2    330  and SpO 2    310  quantities are suitable, then control will be transferred to the initial weaning assessment sub-module  600 , which is discussed in more detail elsewhere herein. 
         [0110]    In the alternative, the oxygenation sub-module  300  and command module  30  assess the P(high) condition  380 . If P(high) is adjusted  390 , then another iteration of the OEELV sub-module  150  is also conducted to support the optimum OEELV sub-module  150  discussed earlier. As control returns to the oxygenation sub-module  300 , P(high) is again assessed  370  to determine whether recruitment sub-module  400  is warranted or whether P(high) must again be adjusted. Assuming for purposes of further illustration that recruitment sub-module  400  is indicated, the oxygenation sub-module  300  relinquishes control to command module  30 , which invokes the recruitment sub-module  400 . 
         [0111]    Referring now also to  FIG. 6 , recruitment sub-module  400  reevaluates the P(high) condition in a different context  420 ,  430 ,  450 , as depicted in more detail in  FIG. 6 . In the circumstance where P(high) becomes greater than 40 cm H 2 O  450 , an alarm signal  410  is sounded to affect immediate intervention. Otherwise, P(high) is adjusted  460 ,  390 ,  480  to improve the pulmonary condition of patient P and the SpO 2  is again iteratively re-examined  310  while recruitment sub-module  400  continues attempts to increase lung surface, reduce dead space, and re-inflate alveolar units as much as possible until SpO 2  values  310  indicate the need for oxygenation sub-module  300 . Feedback of information from other concurrently running modes may be sampled periodically via feedback loop  180  by command module  30 , which can interrupt recruitment as needed and transfer control or invoke a more important mode when required by patient P physiology. For example, if command module  30  detects inbound information from feedback loop  180  describing increased etCO 2  values approaching or exceeding desired limits, control can revoked by command module  30  so that ventilation sub-module  500  can be invoked. 
         [0112]    With continued reference to the previously discussed figures and now also to  FIG. 7 , command module  30  invokes ventilation sub-module  500  to redress an actual or approaching out of limit etCO 2  condition. The ventilation sub-module  500  reevaluates end tidal CO 2  levels  510 , reassesses OEELV conditions, and then assesses patient P breath spontaneity  570  against the set rate or respiratory frequency values obtained from the clinician  110  or automated settings  120 . If breathing spontaneity remains at or below the set rate  570 , then an alveolar ventilation sub-module  504  is affected to adjust T(high)  530 ,  540  and P(high)  370 ,  390  as may be needed to further optimize pulmonary response. 
         [0113]    However, as patient P recovers pulmonary responsiveness and breath spontaneity improves beyond the set rate of, for purposes example without limitation, to a rate of 15 spontaneous breaths over the set rate, then an alveolar ventilation sub-module  504  is effected whereby T(high)  530 , P(high)  370  are adjusted separately, and then in combination  520  for lower values of P(high). For higher values of P(high), the minute ventilation sub-module  506  evaluates Vt  560  to determine whether recruitment sub-module  400  is warranted. If not, then SpO 2  is again verified  310 , T(high) is adjusted  550 , and the patient P is examined against a tachypnea assessment worksheet  590  that is a function of the set rate or respiratory frequency and the actual patient P rate defined in the assessment worksheet  590 . As with other modules, the command module  30  continues to poll for information inbound on the feedback loop  180  so that control can be instantly seized to maintain optimal pulmonary response parameters across the spectrum of continuously monitored variables. 
         [0114]    Attention is now invited also to  FIG. 8  with the hypothetical suggestion that command module  30  recalled control from the ventilation sub-module  500  for another pass through the oxygenation sub-module  300 , and the parameters were evaluated favorably for the command module  30  to invoke the initial weaning assessment sub-module  600 . As with other modules, the FiO 2    330 , SpO 2    310 , etCO 2    510 , breathing spontaneity  570 , and possible tachypnea (spontaneous breathing  15  above the set rate)  580  are re-evaluated. Assuming patient P responds well, then P(high) is assessed  610  and if warranted, the spontaneity of breathing is compared against apnea parameters  620 . The markedly improving patient P will then experience one of the very novel aspects of the inventive ventilator  10  as the command module  30  reconfigures the ventilator  10  away from the mandatory breath control mode and invokes an assisted breathing mode. If the patient P does not respond well, P(high) and T(high) are adjusted  630  and the command module  30  again invokes the initial weaning assessment sub-module  600  to reassess FiO 2    330 , SpO 2    310 , etCO 2    510  and breathing spontaneity  570 ,  580 . 
         [0115]    With reference now also to  FIG. 9 , those knowledgeable in the pertinent fields of expertise will appreciate that the command module  30  invokes an airway positive release ventilation or APRV sub-module  700 , which can be much more comfortable for the recovering pulmonary patient P. Here too, the APRV sub-module  700  re-verifies the pulmonary conditioning of the patient P and examines P(high)  610 . However, unlike other modules, the APRV sub-module  700  institutes a new parameter evaluation set referred to herein as the weaning criteria  710 . These criteria evaluate the patient P against a more rigorous series of critical pulmonary physiological conditions to ensure the patient can withstand the added stresses of substantially less gradual changes in the ventilation sub-module of operation. Before the command module  30  discontinues the mandatory breathing modes of operation, the patient P must pass these weaning criteria  710 . If the patient P fails the weaning criteria  710 , then the command module  30  re-invokes the initial weaning assessment sub-module  600 , or another module if feedback loop  180  alerts the command module  30  to a more urgent requirement. 
         [0116]    Assuming the weaning criteria  710  are met, however, then the patient P is deemed able to withstand greater changes in the pressure-volume slope profile being induced by the ventilator and ventilator system  10 . Accordingly, the APRV sub-module  700  effects additional adjustments  720  to wean or reduce the patient&#39;s P reliance on the mandatory breathing modality of the ventilator  10 . This weaning process and re-evaluation  720 ,  730 ,  710  continues to iterate if well tolerated by the patient P until P(high) is less than or equal to a pressure of only 20 cm H 2 O. At this point, the patient P is recovering well and absent an important indication to the contrary over the feedback loop  180 , the command module  30  again completely reconfigures the operational profiles of the ventilator  10 . 
         [0117]    As illustrated in detail in  FIG. 10 , the commander or command module  30  invokes the CPAP sub-module  800  in a maximum CPAP assistance mode, which speeds up the process of removing the patient P from reliance on the ventilator  10 . P(high) is assessed  810  and the patient P continues to be evaluated against the weaning criteria  710 , and for gross and undesirable deviations from acceptable pulmonary response limits, in which case CPAP is increased  830 . As the patient&#39;s P recovery accelerates, the CPAP sub-module  800  decreases assistance  820 ,  840 ,  850 , until an extubation pressure  860  is reached. Hereafter, the clinician intervenes and extubates the weaned patient P. 
         [0118]    Among many possible modifications to any of the embodiments of the inventive ventilator  10 , one particularly useful variant includes a modified OEELV sub-module (not shown), that can be incorporated as an improvement to the OEELV sub-module  150 , or which may be included as an independent mode capable of operating and cooperating with OEELV sub-module  150 . With continued reference to the various figures and especially to  FIGS. 3   a  and  3   b , and with reference now also now to  FIG. 11 , those having an understanding of the relevant areas of technology may recall that OEELV is derived by using the elements and reference points information acquired during the P(low)/T(low) cycle as is described elsewhere herein. The proposed and optionally preferred OEELV sub-module  150  is ideally functioning for the duration of the ventilation therapy and is operative to continuously optimize EELV, or end expiratory lung volume, of the therapeutic patient P. 
         [0119]    The derived OEELV is a function of disease state (see, e.g.,  FIGS. 3   a  and  3   b ), and the patient&#39;s P pulmonary responsiveness to the oxygenation sub-module  300 , recruitment sub-module  400 , and ventilation sub-module  500 . In a compliant patient P, the OEELV sub-module  150  optimizes EELV by adjusting the T(low) time period. Preferably, the OEELV sub-module  150  also validates the acquired information by using multiple sampling, averaging, and various statistical methods over time for validation and error detection. 
         [0120]    Adjustments of the OEELV are based upon the elements and flow and time reference points acquired during the P(low)/T(low) cycle. Flow and time reference points within the flow/time area, which is established by the P(low)/T(low) cycle, may be used to measure and calculate changes occurring in lung volume during the P(low)/T(low) cycle. For purposes of example and further illustration, but not for purposes of limitation, and looking again to  FIG. 11 , the preferred OEELV sub-module  150  measures the peak expiratory flow rate (PEFR)  1100 , the decay phase  1110 , and the truncation phase  1120  to calculate the angle of deceleration (ADEC) of gas flow and the termination of the flow of gas to determine optimal T(low) adjustment. The OEELV sub-module  150  thereby enables a heretofore unavailable dynamic adjustment, which more accurately and more responsively establishes and maintains the most optimal actual OEELV of the patient P. 
         [0121]    An analysis of  FIG. 11  ought to reveal to those skilled in the arts that an extrapolation phase  1130  may be used to calculate a residual volume and pressure as a function of time. The PEFR  1100  of  FIG. 11  represents the rapid depressurization evidenced by the relaxation and recoil of the thorax after the machine breath. The decay phase  1110  represents the decaying energy drive and the downstream resistance to gas flow. The flow termination phase or truncation phase  1120  establishes the point in the time course of flow where the flow can be determined either as a function of the disease process, or the parameter setting that was input by the user or clinician. The extrapolation phase  1130  can be used graphically and/or algebraically to determine and calculate pressure, volume, and time. 
         [0122]    As described elsewhere herein, and with continued attention to  FIG. 11 , we recall that the OEELV sub-module  150  as well as the OEELV sub-module  150  both measure the peak expiratory flow and the truncation of gas flow, and then uses this information to calculate the ADEC or angle of deceleration, which is in turn used to establish the ideal OEELV value. With this approach, it should be observed that changes in the truncation point will change the angle of deceleration. When the resulting angle becomes less acute, the resultant observation is that recruitment has occurred. Conversely, when the angle becomes more acute, derecruitment is indicated. 
         [0123]    Therefore, the OEELV sub-module  150  suggest adjustments to at least one of P(high), P(low), T(high), or T(low). In the instance where derecruitment is detected, P(high) or T(high) should be increased, or T(low) should be decreased, or some combination thereof should be effected. On the other hand, if recruitment is detected in this way, P(high) should be decreased, T(high) or T(low) should be increased, or some combination thereof should be effected. 
         [0124]    The present invention also contemplates in any of the embodiments of the invention an optimal end inspiratory lung volume (OEILV) sub-module  1200  than can further augment aspects of the recruitment sub-module  400  of  FIG. 6 . In this alternative variation to any of the embodiments of the innovative ventilator and ventilator system  10 , the OEILV sub-module  1200  is optionally or preferably invoked by the command module  30  as needed. More preferably, the OEILV sub-module  1200  is invoked by the recruitment sub-module  400 . Even more preferably, the OEILV sub-module  1200  is invoked by the recruitment sub-module  400  at any moment outside the actual recruitment phases or inspiratory pressurization because the OEILV sub-module  1200  ideally assesses for derecruitment and is active or engaged only during the machine or ventilator  10  breath. Most preferably, the OEILV sub-module  1200  monitors the existing sensor data to identify changes in flow and time during the P(high)/T(high) cycle of ventilation. 
         [0125]    When invoked, the OEILV sub-module  1200  is active over time during the machine breath and acquires recorded reference points of the flow/time course to P(high)/T(high) cycle. The OEILV sub-module  1200  uses this acquired data to identify changes in flow and time coordinate grid during the P(high)/T(high) cycle. If such changes are in fact identified, the OEILV sub-module  1200  may preferably communicate a message to the command module  30 , the recruitment sub-module  400 , and/or over the feedback loop  180 , to initiate recruitment. Even more preferably, the OEILV sub-module  1200  may also suggest and/or effect manual or automated adjustments to P(high) and/or T(high) to further minimize actual or prospective derecruitment and/or to improve the pulmonary conditions of the ventilation therapy and/or the response or conditioning of the patient P. 
         [0126]    In the non-recruitment phase of the recruitment sub-module  400 , the OEILV sub-module  1200 , when active, preferably may also intermittently adjust P(high), T(high), or both, and/or may notify the command module  30 , the feedback loop  180 , and/or other modules of the recommended adjustments, and/or may communicate to the clinician manually or automatically so as to seek clinical intervention if warranted. These adjustments in P(high), T(high), or both, may be applied in an occasional, intermittent, and/or cyclic manner, and may be effected either manually, through informative messages, or through automation. 
         [0127]    In further aspects of the optionally preferred OEILV sub-module  1200 , and with reference also to  FIG. 12 , the OEILV sub-module  1200  may preferably incorporate a resistive element  1210  that occurs during the onset of the machine breath, an inflection point  1250  that correlates with an inflection or a half-way point of the machine breath cycle (the resistive-elastic transition point), and an elastic element  1220  that corresponds with the relaxing subsequent to the machine breath. It is important to note that the OEILV sub-module  1200  measures the inflection point  1250  to determine if the slope of the elastic element  1220  changes. 
         [0128]    In other words, the inquiry seeks to learn whether the elastic element  1220  becomes more acute in derecruitment and less acute in recruitment. Those skilled in the arts may come to understand that the combination of information available from  FIGS. 11 and 12  and the accompanying discussion herein enables a heretofore unavailable means of more accurately discerning whether recruitment has been accomplished or whether derecruitment has occurred. The various modes now available and according to the principles of the invention enable more accurate and more automated systems for better managing and mitigating recruitment and derecruitment during many possible ventilation therapy protocols. 
         [0129]    In any of the embodiments of the inventive ventilator  10  and modes and methods of operation, the breathing spontaneity can be further assessed using an optionally preferred spontaneous breathing sub-module  1340  that is graphically depicted in  FIG. 13 . This spontaneous breathing sub-module  1340  may be further invoked by any of the other modes, modules, and routines of the inventive ventilator  10 . Even so, this spontaneous breathing sub-module  1340  may find special utility in being optionally invoked through the command module  30  alone and/or by either the ventilation sub-module  500  or by the initial weaning assessment sub-module  600 . 
         [0130]    In addition to comparing the actual spontaneous breaths per unit time of the patient P, this sub-module  1340  may preferably assess and analyze the nature of spontaneous breathing to identify and quantify breathing effort, otherwise referred to as the “work of breathing.” More preferably, the spontaneous breathing sub-module  1340  assesses the effect of weaning on the work of breathing. Any of the sensors described elsewhere herein, such as one or more of the strain gauges  68 , can be elastically or tightly affixed to the thorax of the patient P to sense and record movement, and solid-state or similarly capable accelerometers can also be used to gain additional data points that can be used to compute actual work expended to breathe. 
         [0131]    Referring to  FIG. 13  again, such data points can be correlated against a spontaneous breath initiation phase  1360 , a spontaneous peak phase  1370 , and a spontaneous termination phase  1380 . Even more preferably, such data can be adduced during any of the spontaneous breath evaluations  570 ,  580  ( FIGS. 7 and 8 ) occurring during the ventilation and initial weaning assessment sub-modules  500 ,  600 , as well as any other suitable time. These additional indicia of the pulmonary conditioning and response of the patient P can further illuminate the patient&#39;s P true cardiopulmonary physiology, which can lessen the risk that the patient P is prematurely removed from ventilation therapy due to patient P resistance or other issues. 
         [0132]    With continued reference to the various figures and preceding discussion, those knowledgeable in the relevant arts may appreciate that for certain preferred circumstances, the invention also contemplates initiating ventilation of the patient P in an APRV sub-module  700  based on initial oxygenation and ventilation settings. The patient P can then have the safety of the mandatory breath capability of the ventilator  10  while commencing ventilation therapy with a less intrusive profile. The ARPV airway pressure during expiration (P(low)) is substantially zero throughout ventilation to allow for the rapid acceleration of expiratory gas flow rates. Typically, the fraction of oxygen in the inspired gas (FiO 2 ) is initially set at about 0.5 to 1.0 (i.e., about 50% to 100%). The highest airway pressure achieved during inspiration (P(high)) must be sufficiently high to overcome airspace-closing forces and initiate recruitment of lung volume. P(high) may suitably be initialized at a default value of about 35 cm H 2 O. 
         [0133]    Alternatively, P(high) may be established based on either the severity and type of lung injury or the recruitment pressure requirements. The latter method is preferred in cases where the ratio of the partial pressure of oxygen in the blood of the patient P to the fraction of oxygen present in the inspired gas (i.e., PaO 2 /FiO 2 , which is commonly abbreviated as P/F) is less than or equal to about two hundred millimeters of mercury (200 mm Hg). The P/F ratio is preferably monitored continuously. 
         [0134]    Where the type and severity of lung injury are characterized by a P/F of greater than about 350 mm Hg, an initial value of P(high) within the range of about 20 cm H 2 O to 28 cm H 2 O is preferably established. On the other hand, if the P/F ratio is less than about 350 mm Hg, P(high) is preferably initialized within the range of about 28 cm H 2 O to 35 cm H 2 O. 
         [0135]    In situations where the P/F ratio is less than or equal to about 200 mm Hg, which may occur where the patient&#39;s P initial injury is non-pulmonary and/or the lung injury is of an indirect nature, the invention contemplates establishment of P(high) at a value of between about 35 mm Hg and 40 mm Hg but preferably not appreciably above 40 mm Hg. In cases where P(high) is initially established at a default value of about 35 cm H 2 O, P(high) is reduced from such a value once P/F exceeds about 250 mm Hg. Initiation of ventilation also requires the establishment of time (duration) settings for inspiration and expiration. 
         [0136]    Initially, the duration of the positive pressure phase (T(high)) is established at a value within the range of about 5.0 to about 6.0 seconds unless the measured PaCO 2  is greater than about 60 mm Hg. In that case, T(high) is more preferably set to a lower initial value of within the range of about 4.0 to 5.0 seconds. The duration of the ventilator  10  release phase (T(low)) may suitably be initialized at a value within the range of 0.5 to 0.8 seconds with about 0.7 seconds being a preferred default value. 
         [0137]    Once initial values of P(high), P(low), T(high) and T(low) have been established, ventilation continues in a repetitive APRV mode cycle generally as illustrated in  FIG. 14 . During management of ventilation in accordance with the invention, the initial values of one or more of these parameters are re-assessed and modified in accordance with measured parameters as has been described in connection with earlier descriptions. 
         [0138]    In management of ventilation in accordance with the invention, a principal goal is to maintain the level of carbon dioxide in the blood of the ventilated patient P (PaCO 2 ) at a level of less than or equal to about 50 mm Hg. Toward that end, arterial PaCO 2  is monitored continuously or measured as clinically indicated and the ventilator  10  controlled to adjust ventilation as follows. Any time after ventilation has commenced, but preferably soon thereafter or promptly upon any indication of hypercarbia (PaCO 2  above about 50 mm Hg), the setting of T(low) is optionally but preferably checked and re-adjusted if necessary. 
         [0139]    According to the invention, optimal end expiratory lung volume is maintained by titration of the duration of the expiration or release phase by terminating T(low) based on expiratory gas flow. To do so, the flow rate of the expiratory gas is measured by the ventilator  10  and checked in relation to the time at which the controller of the ventilator  10  initiates termination of the release phase. The expiratory exhaust valve should be actuated to terminate the release phase T(low), at a time when the flow rate of the expiratory gas has decreased to about 25% to 50% of its absolute peak expiratory flow rate (PEFR) based on gas flow tracing and pulmonary disease process. An example is illustrated in  FIG. 17 . In that example, T(low) terminates by controlling the expiratory exhaust valve to terminate the release phase when the expiratory gas flow rate diminishes to 40% PEFR. 
         [0140]    If monitoring of PaCO 2  indicates hypocarbia is present (i.e., PaCO 2  less than about 50 mm Hg), T(high) is increased by about 0.5 seconds while maintaining P(high) substantially unchanged. Should the patient P remain hypocarbic as indicated by subsequent measure of PaCO 2 , weaning in the manner to be described may be initiated provided oxygenation is satisfactory and weaning is not otherwise contraindicated based on criteria to be described further below. 
         [0141]    The hypercarbic patient P though is not to be weaned. In the event of hypercarbia, the invention contemplates assessment of the expiratory flow pattern before making significant further adjustments to ventilation parameters. This assessment can readily be carried out by a software program stored within the control unit of the ventilator  10 , which carries out automated analysis of the expiration flow versus time tracing. As illustrated in  FIG. 19 , normal expiratory flow is characterized by flow that declines substantially monotonically from the onset of the release phase through its termination and does not fall off prematurely or abruptly. Restrictive flow in contrast declines rapidly from the onset of the release phase to zero or a relatively small value. Obstructive flow tends to be more extended in duration and is characterized by an inflection point beyond which the rate of flow falls off markedly from its initial rate. 
         [0142]      FIG. 18  illustrates a gas flow pattern with a noticeable inflection point based on analysis of flow data provided by expiratory flow sensors, the control unit of the ventilator  10  is programmed to determine reference points during the P(low)/T(low) cycle. Flow and time reference points within the flow/time area, which is created or established by the P(low)/T(low) cycle, may be used to measure and calculate changes occurring in lung volume during the P(low)/T(low) cycle. If it is determined that obstructive or restrictive flow is present, the invention contemplates adjusting T(low) before making any other significant adjustments to ventilation parameters. This can be done according to either of two alternative methods. 
         [0143]    One method is to adjust T(low) to a predetermined value according to whether flow is either obstructive or restrictive but allowing T(low) to remain at its previous value if flow is normal. In the case of restrictive flow, T(low) should be adjusted to less than about 0.7 seconds. On the other hand, obstructive flow calls for a T(low) of greater duration, preferably greater than about 0.7 seconds with 1.0 to 1.2 being typical. 
         [0144]    It is optional but advisable to promptly assess the sedation level of the hypercarbic patient P. Sedation of the patient P can be evaluated by any suitable technique such as the conventional clinical technique of determining a sedation agitation scale (SAS) score for the patient P. If the patient P appears over-sedated based on the SAS score (SAS score greater than about 2) or otherwise, reduction of sedation should be considered and initiated if appropriate. Thereafter, T(high) should be increased by about 0.5 seconds and P(high) increased concomitantly by about 2 cm H 2 O. After allowing sufficient time for these adjustments to take effect on the patient P, PaCO 2  should be re-evaluated. If the patient P remains hypercarbic, T(high) should be increased again by about 0.5 seconds and P(high) again increased concomitantly by about 2 cm H 2 O. PaCO 2  should then be reassessed and concomitant increases of about 0.5 seconds in T(high) and about 2 cm H 2 O in P(high) repeated until the patient P is no longer hypercarbic. However, the total duration of T(high) should not be increased beyond a maximum of about fifteen (15) seconds. 
         [0145]    Management of oxygenation in accordance with the invention is carried out with the goal of maintaining the level of oxygen in the arterial blood of the ventilated patient P (PaO 2 ) at a value of at least about 80 mm Hg and a maintaining saturation level (SaO 2 ) of at least about 95%. Preferably, fluctuations of PaO 2  are held within a target range of about 55 mm Hg and 80 mm Hg. (Expressed in terms of SpO 2 , the target range would be between about 0.88 and 0.95, although where PaO 2  and SpO 2  data are both available, PaO 2  would take precedence.) Responsive to a determination that oxygenation and saturation both meet the goals just specified, the ventilator  10  would be controlled to progressively decrease the fraction of oxygen in the inspired gas (FiO 2 ) by about 0.5 about every thirty (30) minutes to one (1) hour with the objective of maintaining a blood oxygen saturation level (SaO 2 ) of about 95% at a P(high) of about 35 cm H 2 O and an FiO 2  of about 0.5. Upon meeting the latter objective, weaning in the manner to be described may be initiated provided the ventilation goal described earlier (i.e. a PaCO 2  of less than about 50 mm Hg) is met and weaning is not otherwise contraindicated. 
         [0146]    However, if the goals of oxygenation of PaO 2  of at least about 80 mm Hg and arterial blood oxygen saturation (SaO 2 ) of at least about 95% cannot both be maintained at the then-current FiO 2 , FiO 2  is not decreased. Instead, P(high) is increased to about 40 cm H 2 O and T(high) increased substantially contemporaneously by about 0.5 seconds. 
         [0147]    If such action does not result in raising oxygenation and saturation to at least the goals of PaO 2  of about 80 mm Hg and SaO 2  of about 95%, P(high) is increased to a maximum of about 45 cm H 2 O and T(high) is progressively further increased by about 0.5 seconds to 1.0 seconds. Oxygenation and saturation are then re-evaluated and, if they remain below goal, FiO 2 , if initially less than 1.0, may optionally be increased to about 1.0. Oxygen and saturation continue to be re-evaluated, and T(high) successively raised in increments of about 0.5 to 1.0 seconds until the stated oxygen and saturation goals are met. 
         [0148]    Once those oxygenation and saturation goals are met, ventilation is controlled to maintain those goals while progressively decreasing FiO 2  and P(high) toward the levels at which initiation of weaning can be considered. More particularly, P(high) is decreased by about 1 cm H 2 O per hour while FiO 2  is decreased by about 0.05 about every thirty (30) minutes while maintaining an oxygen saturation of at least about 95%. 
         [0149]    Weaning according to the invention, unless otherwise contraindicated, may commence after the oxygenation and ventilation goals described above have been met. That is, when PaCO 2  remains below about 50 mm Hg and SaO 2  remains at least about 95% at a P(high) of about 35 cm H 2 O and FiO 2 , if previously higher, has been weaned to a level of not greater than about 0.5. During weaning in accordance with the invention, T(high) is controlled to sustain recruitment while P(high) is reduced to gradually reduce airway pressure. As  FIG. 20  illustrates, this is achieved by carrying out a series of successive incremental reductions in P(high) while substantially contemporaneously carrying out a series of successive incremental increases in T(high) so as to induce gradual pulmonary stress relaxation as  FIG. 15  illustrates. 
         [0150]    As a result, the pulmonary pressure versus volume curve shifts progressively from its inspiratory limb to its expiratory limb as illustrated in  FIG. 16 . As can be understood with reference to the previously described figures, weaning may be carried out in two stages, the first of which is more gradual than the second. During the first stage, P(high) is reduced by about 2 cm H 2 O about every hour. Substantially contemporaneously with each reduction in P(high), T(high) is increased by about 0.5 to 1.0 seconds up to, but not in excess of a T(high) of about 15 seconds in total duration. 
         [0151]    As P(high) is being reduced in the manner just described, the fraction of oxygen in the inspired gas (FiO 2 ) is also gradually reduced in accordance with P(high). During the first stage of weaning, this gradual weaning of FiO 2  is carried out gradually. When P(high) has been reduced to about 24 cm H 2 O and FiO 2  weaned to about 0.4 with the patient P sustaining a blood oxygen saturation (SaO 2 ) of at least about 95% weaning may proceed to the more aggressive second stage. The term “substantially contemporaneously” should not be construed to be limited to necessarily require that changes occur precisely at the same moment. Rather, the term is to be construed broadly to encompass not merely events that occur at the same time, but also any which are close enough in time to achieve the advantages or effects described. 
         [0152]    During continued weaning, successive reductions in P(high) and substantially contemporaneous increases in T(high) contemporaneous reductions continue about once every hour. However, during the second stage, the reductions in P(high) take place in increments of about 4 cm H 2 O and the increases in T(high) are each about 2.0 seconds. As reductions in P(high) continue, further weaning of FiO 2  is implemented. Once FiO 2  is weaned to about 0.3, airway pressures are reduced such that the ventilation sub-module by then has been transitioned from APRV to a substantially Continuous Positive Airway Pressure/Automatic Tube Compensation Mode (CPAP/ATC). 
         [0153]    Once the patient P is tolerating CPAP at about 5 cm H 2 O with FiO 2  of not greater than about 0.5, the patient&#39;s P ability to maintain unassisted breathing is assessed, preferably for at least about two (2) hours or more. Criteria for such assessments include: a) SpO 2  of at least about 0.90 and/or PaO 2  of at least about 60 mm Hg; b) tidal volume of not less than about 4 ml/kg of ideal bodyweight; c) respiration rate not significantly above about 35 breaths per minute, and d) lack of respiratory distress, with such distress being indicated by the presence of any two or more of the following: i) Heart rate greater than 120% of the morning-hour rate (though less than about five (5) minutes above such rate may be considered acceptable) ii) marked use of accessory muscles to assist breathing; iii) thoroco-abdominal paradox; iv) diaphoresis and/or v) marked subjective dyspnea. 
         [0154]    If there is an indication of respiratory distress, CPAP at an airway pressure of about 10 cm H 2 O should be resumed and monitoring and reassessment carried out as needed. However, if criteria a) through d) above are all satisfied, the patient P may be transitioned to substantially unassisted breathing such as by extubation with face mask, nasal prong oxygen or room air, T-tube breathing, tracheotomy mask breathing or use of high flow CPAP at about 5 cm H 2 O. 
         [0155]    During all phases of ventilation, including initiation, management and weaning, the patient P should be reassessed at least about every two (2) hours and more frequently if indicated. Blood gas measurements (PaO 2 , SaO 2  and PaCO 2 ) which govern control of ventilation according to the invention should be monitored not less frequently than every two (2) hours though substantially continuous monitoring of all parameters would be ideal. 
         [0156]    Just prior to and during weaning at least one special assessment should be conducted daily, preferably in the morning hours. If not possible to do so, a delay of not more than about four (4) hours could be tolerated. Weaning should not be initiated or continued further unless: (a) at least about 12 hours have passed since initial ventilation settings were established or first changed, (b) the patient P is not receiving neuromuscular blocking agents and is without neuromuscular blockade, and (c) Systolic arterial pressure is at least about 90 mm Hg without vasopressors (other than “renal” dose dopamine). 
         [0157]    If these criteria are all met, a trial should be conducted by ventilating the patient P in CPAP mode at about 5 cm H 2 O and an FiO 2  of about 0.5 for about five (5) minutes. If the respiration rate of the patient P does not exceed about 35 breaths per minute (bpm) during the five (5) minute period weaning as described above may proceed. However, if during the five (5) minute period the respiration rate exceeds about 35 bpm, it should be determined whether such tachypnea is associated with anxiety. If so, administer appropriate treatment for the anxiety and repeat the trial within about four (4) hours. If tachypnea does not appear to be associated with anxiety, resume management of ventilation at the parameter settings in effect prior to the trial and resume management of ventilation as described above. Re-assess at least daily until weaning as described above can be initiated. 
       INDUSTRIAL APPLICABILITY 
       [0158]    The embodiments of the present invention are suitable for use in many respiratory assistance applications that involve the use of ventilators and ventilator systems and methods of operation thereof. The various configurations and capabilities of the inventive ventilator and system and method of operation can be modified to accommodate nearly any conceivable respiratory assistance application and/or requirement. The arrangement, capability, and compatibility of the features and components of the novel ventilators, systems, and methods of operation and use described herein can be readily modified according to the principles of the invention as may be required to suit any particular critical and/or routine care and/or hospital, assisted care, or home care application or situation. Additionally, such inventive ventilators, systems, and methods are suitable for use with nearly all types of ventilation equipment including but not limited to positive pressure or negative pressure respiratory assistance devices. 
         [0159]    Such modifications and alternative arrangements may be further preferred and/or optionally desired to establish compatibility with the wide variety of possible applications that are susceptible for use with the inventive and improved ventilators, respiratory assistance systems, and operational methods that are described and contemplated herein. Accordingly, even though only few such embodiments, alternatives, variations, and modifications of the present invention are described and illustrated, it is to be understood that the practice of such additional modifications and variations and the equivalents thereof, are within the spirit and scope of the invention as defined in the following claims.