Patent Publication Number: US-8122883-B2

Title: Medical ventilator and method of controlling same

Description:
This application is a continuation of U.S. application Ser. No. 10/407,160, filed Apr. 4, 2003 now U.S. Pat. No. 7,066,173; which is a continuation of U.S. application Ser. No. 09/607,713, filed Jun. 30, 2000, now abandoned; which claims the benefit of U.S. Provisional Application Ser. No. 60/141,676, filed Jun. 30, 1999, which are hereby incorporated by reference in its entirety, including all figures, tables, and drawings. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to the respiratory care of a patient and, more particularly, to a ventilator that receives a plurality of ventilator support signals indicative of the sufficiency of ventilation support received by the patient, receives at least one ventilator signal indicative of the ventilator setting of the controls of the ventilator, determines the desired settings of the controls of the ventilator, and regulates the setting of at least one of the controls of the ventilator to provide the appropriate quality and quantity of ventilation support to the patient. 
     2. Background 
     Mechanical ventilatory support is widely accepted as an effective form of therapy and means for treating patients with respiratory failure. Ventilation is the process of delivering oxygen to and washing carbon dioxide from the alveoli in the lungs. When receiving ventilatory support, the patient becomes part of a complex interactive system which is expected to provide adequate ventilation and promote gas exchange to aid in the stabilization and recovery of the patient. Clinical treatment of a ventilated patient often calls for monitoring a patient&#39;s breathing to detect an interruption or an irregularity in the breathing pattern, for triggering a ventilator to initiate assisted breathing, and for interrupting the assisted breathing periodically to wean the patient off of the assisted breathing regime, thereby restoring the patient&#39;s ability to breath independently. 
     In those instances which a patient requires mechanical ventilation due to respiratory failure, a wide variety of mechanical ventilators are available. Most modern ventilators allow the clinician to select and use several modes of inhalation either individually or in combination via the ventilator setting controls that are common to the ventilators. These modes can be defined in three broad categories: spontaneous, assisted or controlled. During spontaneous ventilation without other modes of ventilation, the patient breathes at his own pace, but other interventions may affect other parameters of ventilation including the tidal volume and the baseline pressure, above ambient, within the system. In assisted ventilation, the patient initiates the inhalation by lowering the baseline pressure by varying degrees, and then the ventilator “assists” the patient by completing the breath by the application of positive pressure. During controlled ventilation, the patient is unable to breathe spontaneously or initiate a breath, and is therefore dependent on the ventilator for every breath. During spontaneous or assisted ventilation, the patient is required to “work” (to varying degrees) by using the respiratory muscles in order to breath. 
     The work of breathing (the work to initiate and sustain a breath) performed by a patient to inhale while intubated and attached to the ventilator may be divided into two major components: physiologic work of breathing (the work of breathing of the patient) and breathing apparatus imposed resistive work of breathing. The work of breathing can be measured and quantified in Joules/L of ventilation. In the past, techniques have been devised to supply ventilatory therapy to patients for the purpose of improving patient&#39;s efforts to breath by decreasing the work of breathing to sustain the breath. Still other techniques have been developed that aid in the reduction of the patient&#39;s inspiratory work required to trigger a ventilator system “ON” to assist the patient&#39;s breathing. It is desirable to reduce the effort expended by the patient in each of these phases, since a high work of breathing load can cause further damage to a weakened patient or be beyond the capacity or capability of small or disabled patients. It is further desirable to deliver the most appropriate mode, and, intra-mode, the most appropriate quality and quantity of ventilation support required the patient&#39;s current physiological needs. 
     The early generation of mechanical ventilators, prior to the mid-1960s, were designed to support alveolar ventilation and to provide supplemental oxygen for those patients who were unable to breathe due to neuromuscular impairment. Since that time, mechanical ventilators have become more sophisticated and complicated in response to increasing understanding of lung pathophysiology. Larger tidal volumes, an occasional “sigh breath,” and a low level of positive end-expiratory pressure (PEEP) were introduced to overcome the gradual decrease in functional residual capacity (FRC) that occurs during positive-pressure ventilation (PPV) with lower tidal volumes and no PEEP. Because a decreased functional residual capacity is the primary pulmonary defect during acute lung injury, continuous positive pressure (CPAP) and PEEP became the primary modes of ventilatory support during acute lung injury. 
     In an effort to improve a patient&#39;s tolerance of mechanical ventilation, assisted or patient-triggered ventilation modes were developed. Partial PPV support, in which mechanical support supplements spontaneous ventilation, became possible for adults outside the operating room when intermittent mandatory ventilation (IMV) became available in the 1970s. Varieties of “alternative” ventilation modes addressing the needs of severely impaired patients continue to be developed. 
     The second generation of ventilators was characterized by better electronics but, unfortunately, due to attempts to replace the continuous high gas flow IMV system with imperfect demand flow valves, failed to deliver high flow rates of gas in response to the patient&#39;s inspiratory effort. This apparent advance forced patients to perform excessive imposed work and thus, total work in order to overcome ventilator, circuit, and demand flow valve resistance and inertia. In recent years, microprocessors have been introduced into modern ventilators. Microprocessor ventilators are typically equipped with sensors that monitor breath-by-breath flow, pressure, volume, and derive mechanical respiratory parameters. Their ability to sense and transduce “accurately,” combined with computer technology, makes the interaction between clinician, patient, and ventilator more sophisticated than ever. The prior art microprocessor controlled ventilators suffered from compromised accuracy due to the placement of the sensors required to transduce the data signals. Consequently, complicated algorithms were developed so that the ventilators could “approximate” what was actually occurring within the patient&#39;s lungs on a breath by breath basis. In effect, the computer controlled prior art ventilators were limited to the precise, and unyielding, nature of the mathematical algorithms which attempted to mimic cause and effect in the ventilator support provided to the patient. 
     Unfortunately, as ventilators become more complicated and offer more options, the number of potentially dangerous clinical decisions increases. The physicians, nurses, and respiratory therapists that care for the critically ill are faced with expensive, complicated machines with few clear guidelines for their effective use. The setting, monitoring, and interpretation of some ventilatory parameters have become more speculative and empirical, leading to potentially hazardous misuse of these new ventilator modalities. For example, the physician taking care of the patient may decide to increase the pressure support ventilation (PSV) level based on the displayed spontaneous breathing frequency. This may result in an increase in the work of breathing of the patient which may not be appropriate. This “parameter-monitor” approach, unfortunately, threatens the patient with the provision of inappropriate levels of pressure support. 
     Ideally, ventilatory support should be tailored to each patient&#39;s existing pathophysiology, rather than employing a single technique for all patients with ventilatory failure (i.e., in the example above, of the fallacy of using spontaneous breathing frequency to accurately infer a patient&#39;s work of breathing). Thus, current ventilatory support ranges from controlled mechanical ventilation to total spontaneous ventilation with CPAP for support of oxygenation and the elastic work of breathing and restoration of lung volume. Partial ventilation support bridges the gap for patients who are able to provide some ventilation effort but who cannot entirely support their own alveolar ventilation. The decision-making process regarding the quality and quantity of ventilatory support is further complicated by the increasing knowledge of the effect of mechanical ventilation on other organ systems. 
     The overall performance of the assisted ventilatory system is determined by both physiological and mechanical factors. The physiological determinants, which include the nature of the pulmonary disease, the ventilatory efforts of the patient, and many other physiological variables, changes with time and are difficult to diagnosis. Moreover, the physician historically had relatively little control over these determinants. Mechanical input to the system, on the other hand, is to a large extent controlled and can be reasonably well characterized by examining the parameters of ventilator flow, volume, and/or pressure. Optimal ventilatory assistance requires both appropriately minimizing physiologic workloads to a tolerable level and decreasing imposed resistive workloads to zero. Doing both should insure that the patient is neither overstressed nor oversupported. Insufficient ventilatory support places unnecessary demands upon the patient&#39;s already compromised respiratory system, thereby inducing or increasing respiratory muscle fatigue. Excessive ventilatory support places the patient at risk for pulmonary-barotrauma, respiratory muscle deconditioning, and other complications of mechanical ventilation. 
     Unfortunately, none of the techniques devised to supply ventilatory support for the purpose of improving patient efforts to breath, by automatically decreasing imposed work of breathing to zero and appropriately decreasing physiologic work once a ventilator system has been triggered by a patient&#39;s inspiratory effort, provides the clinician with advice in the increasingly complicated decision-making process regarding the quality and quantity of ventilatory support. As noted above, it is desirable to reduce the effort expended by the patient to avoid unnecessary medical complications of the required respiratory support and to deliver the most appropriate mode, and, intra-mode, the most appropriate quality and quantity of ventilation support required the patient&#39;s current physiological needs. Even using the advanced microprocessor controlled modern ventilators, the prior art apparatus and methods tend to depend upon mathematical models for determination of necessary actions. For example, a ventilator may sense that the hemoglobin oxygen saturation level of the patient is inappropriately low and, from the sensed data and based upon a determined mathematical relationship, the ventilator may determine that the oxygen content of the breathing gas supplied to the patient should be increased. This is similar to, and unfortunately as inaccurate as, a physician simply looking at a patient turning “blue” and determining more oxygen is needed. 
     From the above, in the complicated decision-making environment engendered by the modern ventilator, it is clear that it would be desirable to have a medical ventilator that alerts the clinician of the ventilator&#39;s failure to supply the appropriate quality and quantity of ventilatory support and provides advice to the clinician regarding the appropriate quality and quantity of ventilatory support that is tailored to the patient&#39;s pathophysiology. Further, it would be desirable to have such a ventilator that, in addition to alerting and advising the clinician, also automatically changes the quality and quantity of ventilatory support that is required to support a patient&#39;s current pathophysiology. Such a ventilator is unavailable in current ventilator systems. 
     SUMMARY 
     In accordance with the purposes of this invention, as embodied and broadly described herein, this invention, in one aspect, relates to a method of controlling pulmonary ventilation for a ventilator supplying a breathing gas to a patient via a breathing circuit that is in fluid communication with the lungs of the patient. The ventilator has a plurality of selectable ventilator setting controls governing the supply of ventilation support from the ventilator, each setting control selectable to a level setting. The ventilator preferably receives at least one ventilator setting parameter signal, each ventilator setting parameter signal indicative of the level settings of one ventilator setting control, monitors a plurality of sensors to determine the sufficiency of the ventilation support received by the patient (each sensor generating an output signal), and controls the level settings of the ventilator setting controls in response to the received ventilator setting parameter signal and the output signals. The ventilator preferably utilizes a trainable neural network to determine the desired level settings of the ventilator setting controls. 
     In another aspect, the invention relates to a ventilator that supplies a breathing gas to a patient via a breathing circuit in fluid communication with the ventilator and the lungs of a patient. The ventilator preferably has at least one selectable ventilator setting control, a plurality of sensors, a processing subsystem, and a feedback system. 
     The selectable ventilator setting control governs the supply of ventilation support from the ventilator to the patient via the breathing circuit. Each ventilator setting control generates a ventilator setting parameter signal indicative of the current level setting of the ventilator setting. The sensors measure a plurality of ventilation support parameters and each sensor generates an output signal based on the measured ventilation support parameter. 
     The processing subsystem is connected to receive the output signal from the sensor and the ventilator setting signal(s) from the ventilator setting control(s). The processor of the processing subsystem runs under control of a program stored in the memory of the processing subsystem and determines a desired level setting of at least one ventilator setting control in response to the ventilator setting parameter signal and the output signal. The processor also generates a response signal based on the determination of the desired level setting. The processing subsystem of the ventilator preferably utilizes a trainable neural network to determine the desired level settings of the ventilator setting controls. Responsive to the response signal of the processing subsystem, the feedback system adjusts at least one of the level settings of the ventilator setting controls of the ventilator. 
    
    
     
       DETAILED DESCRIPTION OF THE FIGURES OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principals of the invention. 
         FIG. 1  is a block diagram of one configuration of a ventilator for determining the desired ventilator control settings and regulating the control settings of a ventilator. 
         FIG. 2A  is a block diagram of one configuration of a ventilator showing the ventilator providing ventilation support to a patient connected to the ventilator via a breathing circuit. 
         FIG. 2B  is a block diagram of an embodiment of a ventilator showing the processing system incorporated into the ventilator. 
         FIG. 3  is a block diagram of the ventilator showing a plurality of sensors connected to the processing subsystem of the ventilator. 
         FIG. 4  is a block diagram of a processing subsystem of the present invention. 
         FIG. 5  is a block diagram of a feature extraction subsystem of the present invention. 
         FIG. 6A  is a block diagram of one embodiment of the intelligence subsystem of the processing subsystem of the ventilator. 
         FIG. 6B  is a block diagram of a second embodiment of the intelligence subsystem of the processing subsystem of the ventilator. 
         FIG. 7  is a schematic block diagram of one realization of the processing subsystem of the invention. 
         FIG. 8  is a diagram of the basic structure of an artificial neural network having a layered structure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is more particularly described in the following examples that are intended to be illustrative only since numerous modifications and variations therein will be apparent to those skilled in the art. As used in the specification and in the claims, the singular form “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. 
     As depicted in  FIGS. 1-3 , the ventilator  20  of the present invention preferably comprises at least one selectable ventilator setting control  30 , a processing subsystem  40 , a measuring system, and a feedback system. The ventilator  20  supplies a breathing gas to the lungs of the patient P via a breathing circuit  22  that typically comprises an inspiratory line  23 , an expiratory line  24 , and a patient connection tube  25 , all connected by a patient connector  26 . The preferred ventilator  20  is a microprocessor-controlled ventilator of a type that is exemplified by a Mallinckrodt, Nelcor, Puritan-Bennet, 7200ae, or a Bird 6400 Ventilator. 
     To control the delivery of the breathing gas to the patient P, the preferred ventilator  20  typically has at least one selectable ventilator setting control  30  operatively connected to the processing system  40  for governing the supply of ventilation support provided to the patient P. As one skilled in the art will appreciate, each ventilator setting control is selectable to a desired level setting. Such a ventilator  20  is particularly useful in controlling the delivery of breathing support so that the quantity and quality of ventilation support coincides with the physiological support needs of the patient P. 
     In the preferred embodiment, the preferred ventilator  20  can operate selectively in one or more conventional control modes, as needed and selected by the operator and/or the processing subsystem  40 , including but not limited to: (i) assist control ventilation (ACMV); (ii) sychronized intermittent mandatory ventilation (SDAV); (iii) continuous positive airway pressure (CPAP); (iv) pressure-control ventilation (PCV); (v) pressure support ventilation (PSV); (vi) proportional assist ventilation (PAV); and (vii) volume assured pressure support (VAPS). Further, the setting of one or more conventional controls  30  of the ventilator  20  (i.e., the intra-mode setting controls of the ventilator  20 ) may be adjusted, as needed and selected by the operator and/or the processing system  40  in order to maintain the sufficiency of ventilation support delivered to the patient P. The ventilator setting controls  30  of the ventilator  20  include, but are not limited to, controls for setting: (i) a minute ventilation (Ve) level; (ii) a ventilator breathing frequency (f) level; (iii) a tidal volume (V T ) level; (iv) a breathing gas flow rate (V) level; (v) a pressure limit level; (vi) a work of breathing (WOB) level; (vii) a pressure support ventilation (PSV) level; (viii) a positive end expiratory pressure (PEEP) level; (ix) a continuous positive airway pressure (CPAP) level; and (x) a fractional inhaled oxygen concentration (FIO2) level. 
     The ventilator  20  preferably has a gas delivery system and may also have a gas composition control system. The gas delivery system may, for example, be a pneumatic subsystem  32  in fluid/flow communication with a gas source  34  of one or more breathing gases and the breathing circuit  22  and in operative connection with the ventilator setting controls  30  of the ventilator  20  and the processing subsystem  40 . The breathing circuit  22  is in fluid communication with the lungs of the patient P. As one skilled in the art will appreciate, the pneumatic subsystem  32  of the ventilator  20  and the operative connection of that pneumatic subsystem  32  to the source of breathing gas  34  of the ventilator  20  may be any design known in the art that has at least one actuator (not shown) that is capable of being operatively coupled, preferably electrically coupled, to the ventilator setting controls  30  for control of for example, the flow rate, frequency, and/or pressure of the breathing gas delivered by the ventilator  20  to the patient P from the gas source  34 . Such a pneumatic subsystem  32  is disclosed in U.S. Pat. No. 4,838,259 to Gluck et al., U.S. Pat. No. 5,303,698 to Tobia et al., U.S. Pat. No. 5,400,777 to Olsson et al., U.S. Pat. No. 5,429,123 to Shaffer et al., and U.S. Pat. No. 5,692,497 to Schnitzer et al. all of which are incorporated in their entirety by reference herein, and is exemplified by, for example, the Mallinckrodt, Nelcor, Puritan-Bennet, 7200ae, and the Bird 6400 Ventilator. As one skilled in the art will appreciate, the pneumatic subsystem  32  may be operatively coupled to the processing subsystem  40  of the ventilator  20  and may be responsive to the processing subsystem  40  without the intervening step of controlling/regulating the ventilator controls  30 . 
     The gas composition control system may for example be an oxygen-control subsystem  36  coupled to the source of breathing gas  34  and in operative connection to the ventilator setting controls  30  of the ventilator  20  and the processing subsystem  40 . The oxygen control subsystem  36  allows for the preferred control of the percentage composition of the gases supplied to the patient P. As one skilled in the art will appreciate, the oxygen control subsystem  36  of the ventilator  20  and the operative connection of that oxygen control subsystem  36  to the pneumatic subsystem  32  and to the source of breathing gas  34  of the ventilator  20  may be any design known in the art that has at least one actuator (not shown) that is capable of being operatively coupled, preferably electrically coupled, to the ventilator setting controls  30  for control of, for example, the percentage composition of the oxygen supplied to the patient P. As one skilled in the art will further appreciate, the oxygen control subsystem  36  may be operatively coupled to the processing subsystem  40  of the ventilator  20  and may be responsive to the processing subsystem  40  without the intervening step of controlling the ventilator controls  30 . 
     The processing subsystem  40  of the ventilator  10  preferably has an input  44  that is operatively coupled to the ventilator setting controls  30  of the ventilator  20  so that at least one ventilator setting parameter signal  42  may be received by the processing subsystem  40  of the ventilator  20 . Each ventilator setting parameter signal  42  is preferably indicative of the current level setting of one ventilator setting control  30 . Thus, the processing system  40  is in receipt of ventilator setting parameter signals  42 , preferably continuously, indicative of the current level settings of the ventilator controls  30 . As one skilled in the art will appreciate, the current level settings of the ventilator control settings  30  may be stored in the memory of the processing subsystem  40 . In this example, the ventilator setting parameter signals  42  would be input from the memory of the processing subsystem  40  to the processor for continued processing and assessment. 
     For example, the input of the processing system  40  may receive one or more of the following ventilator setting parameter signals  42 : a minute ventilation (V E ) signal indicative of the V E  level set on the ventilator  20 ; a ventilator breathing frequency (f) signal indicative of the f level set on the ventilator  20 ; a tidal volume (V T ) signal indicative of the V T  level set on the ventilator  20 ; a breathing gas flow rate (V) signal indicative of the V level set on the ventilator  20 ; a pressure limit signal indicative of the pressure limit set on the ventilator  20 ; a work of breathing (WOB) signal indicative of the WOB level set on the ventilator  20 ; a pressure support ventilation (PSV) signal indicative of the PSV level set on the ventilator  20 ; a positive end expiratory pressure (PEEP) signal indicative of the PEEP level set on the ventilator  20 ; a continuous positive airway pressure (CPAP) signal indicative of the CPAP level set on the ventilator  20 ; and a fractional inhaled oxygen concentration (FIO2) signal indicative of the FIO2 level set on the ventilator  20 . 
     The measuring system of the ventilator  20  is also operatively connected to the processing subsystem  40 . The measuring system senses and measures select ventilation support parameters which are indicative of the ventilation support provided to the patient P and the physiological condition of the patient P. It is contemplated that the measuring system may comprise at least one sensor  52 , and preferably comprises a plurality of sensors  52 , for capturing the desired ventilation support data. Each sensor  52  generates an output signal  51  based on the particular measured ventilator support parameter. In one preferred embodiment shown in  FIG. 3 , the processing subsystem  30  is shown operatively connected to a flow rate sensor  53 , a exhaled CO2 (Ex CO2) sensor  54 , a pressure sensor  55 , a blood pressure sensor  56 , and a SPO2 sensor  57 . In this embodiment, it is preferred that the ventilator  20  be responsive to the output signals  51  input into the processing subsystem  40  from: i) the flow rate sensor  53  which is indicative of the flow rate ventilation support parameter of the gas expired/inspired by the patient P within the breathing circuit  22 , ii) the gas pressure sensor  55  which is indicative of the pressure ventilation support parameter of the breathing gas within the breathing circuit  22 , and iii) the Ex CO2 sensor  54  which is indicative of the exhaled carbon dioxide ventilation support parameter present in the exhaled gas expired by the patient P within the breathing circuit  22  (i.e., the flow rate output signal  51  generated by the flow rate sensor  53 , the gas pressure output signal  51  generated by the gas pressure sensor  55 , and the Ex CO2 output signal  51  generated by the Ex CO2 sensor  54 ). Optionally, the ventilator  20  may be responsive to the output signals  51  input into the processing subsystem  40  from the output of the blood pressure sensor  56 , which is indicative of the blood pressure ventilation support parameter of the patient P, for example the arterial systolic, diastolic, and mean blood pressure of the patient P, and the SPO2 sensor  57  which is indicative of the hemoglobin oxygen saturation level ventilation support parameter of the patient P (i.e., the blood pressure output signal  51  generated by the blood pressure sensor  56  and the SPO2 output signal  51  generated by the SPO2 sensor  57 ). 
     The flow rate sensor  53 , the pressure sensor  55 , and the Ex CO2 sensor  54  are preferably positioned between the patient connector  26  and the patient connection tube  25 . Alternatively, it is preferred that the pressure sensor  55  be located at the tracheal end of the patient connection tube  25 . The flow rate, pressure, and Ex CO2 sensors  53 ,  55 ,  54  are exemplified by Novametrics, CO 2 SMO+ monitor (which has a flow rate, pressure and Ex CO2 sensors). The blood pressure sensor  56  and the SPO2 sensor  57  are exemplified by Dynamap, Inc.&#39;s blood pressure sensor and Novametrics, CO 2 SMO+ monitor&#39;s SPO2 sensor. The blood pressure sensor  56  and the SPO2 sensor  57  may be attached to a portion of the patient&#39;s body to render the requisite measurements. For example, the blood pressure sensor  56 , here for example shown as a blood pressure cuff, is shown attached to the arm of the patient P and the SPO2 sensor  57 , which may, for example, be a pulse oximeter, is shown attached to a finger of the patient P. One skilled in the art will appreciate that the blood pressure data may be derived from the SPO2 sensor  57  which eliminates the need for the blood pressure sensor  56 . 
     Additional standard equipment can include an operator interface  60 , which in the preferred embodiment is a membrane keypad, a keyboard, a mouse, or other suitable input device, for providing user inputs of both data and control commands needed to execute the software which implements the various functions of the invention. The operator of the ventilator  20  of the present invention may provide the processing subsystem  40 , via an operator input signal  61  generated by the operator interface  60 , with any number of applicable input parameters, such as patient identification information, patient age, patient weight, or other desired patient statistics. It is preferred that the operator input predetermined patient reference data, such as the arterial blood gas ph, the arterial blood gas PaO2, and/or the arterial blood gas PaCO2 of the patient&#39;s blood, and/or patient&#39;s temperature into the processing subsystem  40  as operator input signals  61  via the operator interface  60 . The ventilator  20  may also be responsive to the core body temperature of the patient P, which may be input into the processing subsystem  40  as an output signal  51  from a temperature sensor  58  attached to the patient P or as an operator input signal  61  via the operator interface  60 . 
     The processing subsystem  40  preferably comprises a processor  46 , for example a microprocessor, a hybrid hard/software system, controller, computer, and a memory. The output-signals  51  and ventilation data  72  derived from the output signals  51  are stored in the memory of the processing subsystem  40  at user-defined rates, which may be continuous, for as-needed retrieval and analysis. The ventilator setting signal  42  may also be stored in the memory at a user-defined rate. As one skilled with the art will appreciate, any generated signal may be stored in the memory at user-defined rates. The memory may be, for example, a floppy disk drive, a CD drive, internal RAM or hard drive of the associated processor  46 . 
     The processing subsystem  40  is responsive to the output signals  51  of the measuring means, the ventilator setting parameter signal  42 , and, if provided, the operator input signal  61 . The processor  46  of the processing subsystem  40  runs under the control of a program stored in the memory and has intelligent programming for the determination of at least one desired level setting of the ventilator control settings  30  based on at least a portion of the output signals  51  from the measuring system, at least a portion of ventilator setting parameter signal(s)  42  received at the input  44  of the processing subsystem  40 , and, if provided, at least a portion of the operator input signal  61 . Based on the determination of the desired level settings of the ventilator controls  30 , the processing means  40  generates a response signal  49 . 
     The desired level settings for the ventilator setting controls  30  of the ventilator  20  may include at least one of the group of: i) a minute ventilation (V E ) level indicative of the desired V E  level to set on the ventilator  20 ; ii) a ventilator breathing frequency (f) level indicative of the desired f level to set on the ventilator  20 ; iii) a tidal volume (V T ) level indicative of the V T  level to set on the ventilator  20 ; iv) a breathing gas flow rate (V) level indicative of the V level to set on the ventilator  20 ; v) a pressure limit level indicative of the pressure limit level to set on the ventilator  20 ; vi) a work of breathing (WOB) level indicative of the WOB level to set on the ventilator  20 ; vii) a pressure support ventilation (PSV) level indicative of the PSV level to set on the ventilator  20 ; viii) a positive end expiratory pressure (PEEP) level indicative of the PEEP level to set on the ventilator  20 ; ix) a continuous positive airway pressure (CPAP) level indicative of the CPAP level to set on the ventilator  20 ; and x) a fractional inhaled oxygen concentration (FIO2) level indicative of the FIO2 level to set on the ventilator  20 . 
     The processing subsystem  40  controls the delivery of breathing gas supplied to the patient P by regulating the level setting, or level settings, of the ventilator setting controls  30 . This control occurs using the feedback system, which is responsive to the response signal  49  of the processing subsystem  40 . The feedback system adjusts at least one of the ventilator setting controls  30  of the ventilator  20  so that level settings of the ventilator setting controls  30  correspond to the determined desired level settings for the ventilator controls  30 . 
     Preferably, the feedback system comprises at least one driver circuit  100  electrically coupled to the processing subsystem  40  and also electrically coupled to each ventilator setting control  30 . The driver circuits  100  adjust the ventilator setting controls  30  based on electrical signals received from the processing subsystem  40 , thus varying the ventilator setting controls  30  of the ventilator  20 . In one example, the ventilator setting controls  30  are responsive to the response signal  49  and generates a driver signal  102  to the pneumatic subsystem  32  to regulate the actuators of the pneumatic subsystem  32  to control the breathing gas supplied to the patient P (i.e., to control the flow rate, pressure, and/or frequency, etc., of the gas supplied). The ventilator setting controls  30  may also be responsive to the response signal  49  to generate a driver signal  102  to the oxygen control subsystem  36  to regulate the actuators of the oxygen control subsystem  36  to control the percentage composition of the gases being supplied to the patient P. Thus, in order to maintain the sufficiency of the ventilation support provided to the patient P, it is preferred that the feedback means adjust at least one of the ventilator controls  30  to vary at least one level setting selected from the group comprising: i) a minute ventilation (V E ) level; ii) a ventilator breathing frequency (f) level; iii) a tidal volume (V T ) level; iv) a breathing gas flow rate (V) level; v) a pressure limit level; vi) a work of breathing (WOB) level; vii) a pressure support ventilation (PSV) level; viii) a positive end expiratory pressure (PEEP) level; ix) a continuous positive airway pressure (CPAP) level; and x) a fractional inhaled oxygen concentration (FIO2) level. 
     The desired ventilator level settings determined by the processing system  40  of the ventilator  20  may be displayed to the operator via a display  62 . The display of the ventilator  20  preferably comprises a visual display  62  or CRT, electronically coupled to the processing subsystem  40  for outputting and displaying output display signals generated from the processing subsystem  40 . 
     Still further, the ventilator  20  may have an alarm  21  for alerting the operator of either a failure of the ventilator  20 , such as a power failure of loss of signal data input, or an inappropriate setting of a ventilator control  30 , such as a level setting of a ventilator setting control  30  currently controlling the delivery of ventilator support to the patient P differing from a recommended desired level setting for the ventilator setting control  30 , or to indicate a change in the ventilator setting control  30 , such as a ventilator setting control  30  being regulated in response to closed-loop control from the processing subsystem  40 . Preferably, the alarm  21  comprises a visual and/or audio alarm, but any means for alerting the operating clinician known to one skilled in the art may be used. Of course, it is desired to use a backup power supply, such as a battery. 
     Referring to  FIGS. 4 and 5 , the processing subsystem  40  of the preferred embodiment of the present invention has a means for determining the desired ventilation level settings for the controls  30  of the ventilator  20 . The determining means preferably comprises a feature extraction subsystem  70  and an intelligence subsystem  80 . The feature extraction subsystem  70  has a means for extracting and compiling pertinent ventilation data features from the input of the measuring means (i.e., the output signals  51 ). In effect, the feature extraction subsystem  70  preferably acts as a preprocessor for the intelligence subsystem  80 . An example of the feature extraction subsystem  70  is shown in  FIG. 5 . Here, a flow rate sensor  53 , a gas pressure sensor  55 , a SPO2 sensor  57 , an Ex CO2 sensor  54 , a temperature (T) sensor  58 , a blood pressure (BP) sensor  56 , of a type described above, and any other desired sensor are operatively connected to the feature extraction subsystem  70  of the processing subsystem  40 . Preferably, the flow, rate sensor  53 , the gas pressure sensor  55 , and the Ex CO2 sensor  54  provide the only inputs to the monitor system. The other sensor inputs, and the user input, may be included to increase the reliability and confidence of the determined desired level settings of the controls  30 . The processing system  40  of the ventilator  20  preferably adjusts the extraction of ventilator data  72  as a function of the presence or absence of these optional inputs. By making the number of inputs optional, which also makes the required number of sensors  52  comprising the measuring system optional, the number of environments in which the ventilator  20  can be used is increased. 
     The purpose of the feature extraction subsystem  70  is to calculate and/or identify and extract important variables or features from the output signals  51  produced by the measuring means. For example, from the exemplified required inputs to the feature extraction subsystem  70 , i.e., the gas pressure output signal  51 , the flow rate output signal  51 , and the Ex CO2 output signal  51 , a plurality of ventilation data  72  may be derived. The derived ventilation data  72  may comprise: the values of any output signals  51  used, such as, for example, the gas pressure output signal  51 , the flow rate output signal  51 , and the Ex CO2 output signal  51  output signals  51 ; the peak inflation pressure (PIP), which is the maximal pressure generated during mechanical ventilation of the lungs; the mean airway pressure (PAW), which is the average positive pressure measured at the airway opening in the patient connection tube  25  or in the breathing circuit  22  over one minute; the positive end expiratory pressure (PEEP), which is the baseline or starting positive pressure prior to mechanical inflation or the positive pressure applied continuously during inhalation and exhalation during spontaneous ventilation; breathing frequency (f), which is the frequency or rate or breathing per minute (the total breathing frequency f TOT  is the sum of the mechanical f MECH  ventilator preselected frequency and the spontaneous f SPON  patient breathing frequency); the tidal volume (V T ), which is the volume of the breathing gas moving in and out of the lungs per breath (V T MECH  is the ventilator preselected V T  per breath and V T SPON  is the inhaled and exhaled volume per breath of the patient); the minute exhaled ventilation (V E ), which is the volume of breathing gas moving in and out of the lungs of the patient per minute (V E  is the product of the breathing frequency f and the tidal volume (V E =f×V T ), and the V E TOT  is the sum of the ventilator preselected V E  (V E MECH ) and the spontaneous patient V E  inhaled and exhaled per minute (V E SPON )); the inhalation-to-exhalation time ratio (I:E ratio), which is the ratio of inhalation time to exhalation time during mechanical ventilation; the physiologic dead space volume (V Dphys ), which is the volume of gas in the anatomic airway and in ventilated, unperfused alveoli that does not participate in blood gas exchange; the lung carbon dioxide elimination rate (LCO2), which is the volume of CO2 exhaled per breath or per minute (LCO2 is the area under the Ex CO2 and volume curve); the partial pressure end-tidal carbon dioxide level (PetCO2), which is the partial pressure of the exhaled CO2 measured at the end of the exhalation; the cardiac output (CO) of the patient P, which is the amount of blood ejected from the heart per minute and which may, for example be derived from the determined LCO2 rate; the respiratory system compliance and resistance; the respiratory muscle pressure, the work of breathing of the patient P which may be derived from the determined respiratory muscle pressure; and pressure-volume loops. 
     Ventilation data  72  may also be derived from the exemplified optional inputs to the feature extraction subsystem  70 . From the SPO2 output signal  51 , the arterial blood hemoglobin oxygen saturation level and the heart rate may be determined, and the pulsatile blood pressure waveform of the SPO2 output signal  51  may be used to determine arterial blood pressure. Additionally, from the blood pressure output signal  51 , the arterial systolic, diastolic and mean blood pressure of the patient P may be determined. Further, from the temperature output signal  51 , the core body temperature of the patient P may be derived. Still further, from the arterial blood hemoglobin oxygen saturation level and the determined LCO2, the dead space volume may be determined. 
     The feature extraction subsystem  70  may also receive user input via the operator interface  60  and may receive the ventilator setting parameter signal  42 . The ventilation data  72  is preferably compiled in the feature extraction subsystem  70  and a feature vector  74  or matrix is preferably generated which contains all of the ventilation data items used by the ventilator  20  to perform the ventilation support assessment and ventilator level setting determination process. The feature vector  74  may be updated at user-defined intervals such as, for example, after each breath or each minute and is output from the feature extraction subsystem  70  to the intelligence subsystem  80  as a ventilation data output signal  75 . Alternatively, as one skilled in the art will appreciate, the ventilation data  72  may be directly outputted to the intelligence subsystem  80  as the ventilation data output signal  75  without the intervening step of generating the feature vector  74  or matrix. The ventilation data  72  may also be outputted to the display  62 . 
     Referring to  FIGS. 4 ,  6 A and  6 B, the intelligence subsystem  80  of the processing subsystem  40  preferably has a neural network  82 . The primary function of the intelligence subsystem  80  is to make an assessment of the ventilator support provided to the patient and, based upon the assessment, recommend the desired ventilator level settings of the controls  30  of the ventilator  20  which will adequately, and preferably optimally, support the physiological ventilation support needs of the patient P. Further, the intelligence subsystem  80  regulates the feedback means of the ventilator  20  in response to the determined desired level settings of the controls  30 . For example, as shown in  FIG. 6A , the intelligence subsystem  80  of the processing subsystem  40  may have a neural network  82  that receives the ventilation data output signal  75  containing the compiled ventilation data  72 . The neural network  82  also receives the ventilator setting parameter signal  42  and may receive user input from the operator interface  60 . 
     To fully appreciate the various aspects and benefits produced by the present invention, a basic understanding of neural network technology is required. Following is a brief discussion of this technology, as applicable to the ventilator  20  and method of the present invention. 
     Artificial neural networks loosely model the functioning of a biological neural network, such as the human brain. Accordingly, neural networks are typically implemented as computer simulations of a system of interconnected neurons. In particular, neural networks are hierarchical collections of interconnected processing elements configured, for example, as shown in  FIG. 8 . Specifically,  FIG. 8  is a schematic diagram of a standard neural network  82  having an input layer  84  of processing elements, a hidden layer  86  of processing elements, and an output layer  88  of processing elements. The example shown in  FIG. 8  is merely an illustrative embodiment of a neural network  82  that can be used in accordance with the present invention. Other embodiments of a neural network  82  can also be used, as discussed next. 
     Turning next to the structure of a neural network  82 , each of its processing elements receives multiple input signals, or data values, that are processed to compute a single output. The output value is calculated using a mathematical equation, known in the art as an activation function or a transfer function that specifies the relationship between input data values. As known in the art, the activation function may include a threshold, or a bias element. As shown in  FIG. 8 , the outputs of elements at lower network levels are provided as inputs to elements at higher levels. The highest level element, or elements, produces a final system output, or outputs. 
     In the context of the present invention, the neural network  82  is a computer simulation that is used to produce a recommendation of the desired ventilator level settings of the controls  30  of the ventilator  20  which will adequately, and preferably optimally, support the physiological ventilation support needs of the patient, based upon at least a portion of the available ventilator setting parameter signals  42  and at least a portion of the ventilation data output signal  75  (i.e., at least a portion of the ventilation data  72 ). 
     The neural network  82  of the present invention may be constructed by specifying the number, arrangement, and connection of the processing elements which make up the network  82 . A simple embodiment of a neural network  82  consists of a fully connected network of processing elements. The processing elements of the neural network  82  are grouped into layers: an input layer  84  where at least a portion of the ventilation data output signal  75  and the selected ventilator setting parameter signals  42  are introduced; a hidden layer  86  of processing elements; and an output layer  88  where the resulting determined level setting(s) for the ventilator setting control(s)  30  is produced. The number of connections, and consequently the number of connection weights, is fixed by the number of elements in each layer. 
     In a preferred embodiment of the present invention, the data types provided at the input layer may remain constant. In addition, the same mathematical equation, or transfer function, is normally used by the elements at the middle and output layers. The number of elements in each layer is generally dependent on the particular application. As known in the art, the number of elements in each layer in turn determines the number of weights and the total storage needed to construct and apply the network  82 . Clearly, more complex networks  82  generally require more configuration information and therefore more storage. 
     In addition to the structure illustrated in  FIG. 6A , the present invention contemplates other types of neural network configurations for the neural network module such as the example shown in  FIG. 6B , which is described in more detail below. All that is required by the present invention is that a neural network  82  be able to be trained and retrained, if necessary, for use to determine the desired ventilator level settings of the controls  30  of the ventilator  20 . It is also preferred that the neural network  82  adapt (i.e., learn) while in operation to refine the neural network&#39;s  82  determination of the appropriate level settings for the controls  30  of the ventilator  20 . 
     Referring back to  FIGS. 6A and 8 , the operation of a specific embodiment of a feedforward neural network  82  is described in more detail. It should be noted that the following description is only illustrative of the way in which a neural network  82  used in the present invention can function. Specifically, in operation, at least a portion of selected ventilation data  72  from the ventilation data output signal  75  and the selected ventilator setting parameter signals  42  (i.e., collectively the input data) is provided to the input layer  84  of processing elements, referred to hereafter as inputs. The hidden layer elements are connected by links  87  to the inputs, each link  87  having an associated connection weight. The output values of the input processing elements propagate along these links  87  to the hidden layer  86  elements. Each element in the hidden layer  86  multiplies the input value along the link  87  by the associated weight and sums these products over all of its links  87 . The sum for an individual hidden layer element is then modified according to the activation function of the element to produce the output value for that element. In accordance with the different embodiments of the present invention the processing of the hidden layer elements can occur serially or in parallel. 
     If only one hidden layer  86  is present, the last step in the operation of the neural network is to compute the output(s), or the determined ventilator level setting(s) of the control(s)  30  of the ventilator  20  by the output layer element(s). To this end, the output values from each of the hidden layer processing elements are propagated along their links  87  to the output layer element. Here, they are multiplied by the associated weight for the link  87  and the products are summed over all links  87 . The computed sum for an individual output element is finally modified by the transfer function equation of the output processing element. The result is the final output or outputs which, in accordance with a preferred embodiment of the present invention, is the desired level setting or level settings of the ventilator controls  30 . 
     In the example of the intelligence subsystem  80  shown in  FIG. 6B , the intelligence subsystem  80  is a hybrid intelligence subsystem that contains both rule-based modules  90  as well as neural networks  82 . In this alternative embodiment of the intelligence subsystem  90 , the determination of the desired level settings of the ventilator setting controls  30  are broken down into a number of tasks that follow classical clinical paradigms. Each task may be accomplished using a rule-based system  90  or a neural network  82 . In the preferred configuration, the determination of desired level settings of the ventilator setting controls  30  are performed by one of a series of neural networks  82 . 
     The purpose of the ventilation status module  92  is to make an initial assessment of the adequacy of the ventilation support being provided to the patient P based on the level settings of the ventilation controls  30  (as inputted to the intelligence subsystem  80  by the ventilator setting parameter signals  42 ) and the ventilation data output signal  75 . The final determination of the desired ventilator level settings of the controls  30  is accomplished by one of a series of available neural networks  82  in the ventilator control setting predictor module  94 . The purpose of the rule-based front end  96  is to determine based on inputs from the ventilation status module  92 , data entered by the operator, and the ventilator setting parameter signal  42 , which of the available neural networks  82  will determine the desired settings of the controls  30 . The rule-based front end  96  will also determine which inputs are extracted from the ventilation data output signal  75  and presented to the selected neural network  82 . Inputs to the ventilator control setting predictor module  94  include ventilation data  72  from the ventilation data output signal  75 , user input, and input from the ventilator setting parameter signals  42 . The purpose of the rule-based back end module  98  is to organize information from previous modules, neural networks  82 , user input, and ventilation data  72  in the ventilation data output signal  75  and to format the information for display on the visual display  62  as well as for storage to an external storage  64  such as a disk file. 
     As with most empirical modeling technologies, neural network development requires a collection of data properly formatted for use. Specifically, as known in the art, input data and/or the outputs of intermediate network processing layers may have to be normalized prior to use. It is known to convert the data to be introduced into the neural network  82  into a numerical expression, to transform each of the numerical expressions into a number in a predetermined range, for example by numbers between 0 and 1. Thus, the intelligent subsystem  80  of the present invention preferably has means for: i) selecting at least a portion of the ventilation data  72  from the ventilation data output signal  75  and at least a portion of the ventilator setting parameter signals  42 , ii) converting the selected portion of the ventilation data  72  and the selected portion of the ventilator setting parameter signals  42  into numerical expressions, and iii) transforming the numerical expressions into a number in a predetermined range. 
     In one conventional approach which can also be used in the present invention, the neural network  82  of the present invention may include a preprocessor. The preprocessor extracts the correct data from the processing subsystem memory means and normalizes each variable to ensure that each input to the neural network  82  has a value in a predetermined numerical range. Once the data has been extracted and normalized, the neural network  82  is invoked. Data no normalization and other formatting procedures used in accordance with the present invention are known to those skilled in the art and will not be discussed in any further detail. 
     In accordance with a preferred embodiment of the present invention the neural network  82  is trained by being provided with the ventilator control setting assessment made by a physician and with input data, such as ventilation data  72 , the ventilator setting parameter signals  42 , and the output signals  51  that were available to the physician. In the sequel the assessment along with the corresponding input measurement and input data is referred to as a data record. All available data records, possibly taken for a number of different patients, comprise a data set. In accordance with the present invention, a corresponding data set is stored in the memory and is made available for use by the processing subsystem  40  for training and diagnostic determinations. 
     A typical training mechanism used in a preferred embodiment of the present invention is briefly described next. Generally, the specifics of the training process are largely irrelevant for the operation of the ventilation monitor system. In fact, all that is required is that the neural network  82  be able to be trained and retrained, if necessary, such that it can be used to determine acceptably accurate determinations of desired level settings of the controls  30 . Neural networks  82  are normally trained ahead of time using data extracted from patients  10  by other means. Using what it has learned from the training data, the neural network  82  may apply it to other/new patients P. 
     As known in the art, a myriad of techniques has been proposed in the past for training feedforward neural networks. Most currently used techniques are variations of the well-known error back-propagation method. The specifics of the method need not be considered in detail here. For further reference and more detail the reader is directed to the excellent discussion provided by Rumelhardt et al. in “Parallel Distributed Processing: Explorations in the Microstructure of Cognition,” vols. 1 and 2, Cambridge: MIT Press (1986), and “Explorations in Parallel Distributed Processing, A Handbook of Models, Programs, and Exercises,” which are incorporated herein in their entirety by reference. 
     Briefly, in its most common form back-propagation learning is performed in three steps: 
     1. Forward pass; 
     2. Error back-propagation; and 
     3. Weight adjustment. 
     As to the forward pass step, in accordance with the present invention a single data record, which may be extracted from the ventilation data output signal  75 , is provided to the input layer  84  of the network  82 . This input data propagates forward along the links  87  to the hidden layer elements which compute the weighted sums and transfer functions, as described above. Likewise, the outputs from the hidden layer elements are propagated along the links to the output layer elements. The output layer elements computes the weighted sums and transfer function equations to produce the desired level settings of the ventilator controls  30 . 
     In the following step of the training process, the physician assessment associated with the data record is made available. At that step, the determination of the desired level settings of the ventilator setting controls  30  produced by the neural network  82  is compared with the physician&#39;s assessment. Next, an error signal is computed as the difference between the physician&#39;s assessment and the neural network&#39;s  82  determination. This error is propagated from the output element back to the processing elements at the hidden layer  86  through a series of mathematical equations, as known in the art. Thus, any error in the neural network output is partially assigned to the processing elements that combined to produce it. 
     As described earlier, the outputs produced by the processing elements at the hidden layer  86  and the output layer  88  are mathematical functions of their connection weights. Errors in the outputs of these processing elements are attributable to errors in the current values of the connection weights. Using the errors assigned at the previous step, weight adjustments are made in the last step of the back-propagation learning method according to mathematical equations to reduce or eliminate the error in the neural network determination of the desired level settings of the ventilator controls  30 . 
     The steps of the forward pass, error back-propagation, and weight adjustment are performed repeatedly over the records in the data set. Through such repetition, the training of the neural network  82  is completed when the connection weights stabilize to certain values that minimize, at least locally, the determination errors over the entire data set As one skilled in the art will appreciate however, the neural network  82  may, and preferably will continue to train itself (i.e., adapt itself) when placed into operational use by using the data sets received and stored in the memory of the processing subsystem  40  during operational use. This allows for a continual refinement of the ventilator  20  as it is continually learning, i.e., training, while in operational use. Further, it allows for the continual refinement of the determination of the appropriate ventilator level settings in regard to the particular patient P to which the ventilator is operatively attached. 
     In addition to back-propagation training, weight adjustments can be made in alternate embodiments of the present invention using different training mechanisms. For example, as known in the art, the weight adjustments may be accumulated and applied after all training records have been presented to the neural network  82 . It should be emphasized, however, that the present invention does not rely on a particular training mechanism. Rather, the preferred requirement is that the resulting neural network  82  produce acceptable error rates in its determination of the desired level settings of the ventilator setting controls  30 . 
     Upon completion of the determination of the desired level settings of the ventilator setting controls  30  by the intelligent subsystem  80  of the processing system  40 , the desired ventilator level settings of the ventilator setting controls  30  may be displayed on the visual display  62  for use by the physician. The stored ventilation data output signal  75 , and particularly the subset of the ventilation data output signal containing the ventilation data  72  that was used by the intelligent subsystem  80  in the determination of the desired ventilator level settings, may be provided to the visual display  62 . Also, the stored ventilator setting parameter signals  42  and the stored output signals  51  may be displayed on the visual display  62  in an appropriate format. At this point, the physician can review the results to aid in her or his assessment of the desirability of the recommended desired level settings of the ventilator setting controls  30 . The displayed results can be printed on printer (not shown) to create a record of the patient&#39;s condition. In addition, with a specific preferred embodiment of the present invention, the results can be communicated to other physicians or system users of computers connected to the ventilator  20  via an interface (not shown), such as for example a modem or other method of electronic communication. 
     Additionally, a preferred embodiment the present invention provides a method and apparatus for a real-time ventilator  20 . Real-time operation demands, in general, that input data be entered, processed, and displayed fast enough to provide immediate feedback to the physician in the clinical setting. In alternate embodiments, off-line data processing methods can be used as well. In a typical off-line operation, no attempt is made to respond immediately to the physician. The measurement and interview data in such case is generated some time in the past and stored for retrieval and processing by the physician at an appropriate time. It should be understood that while the preferred embodiment of the present invention uses a real-time approach, alternative embodiments can substitute off-line approaches in various steps. 
     The preferred method of operation of the present invention comprises the steps of receiving at least one ventilator setting parameter signal  42  indicative of the current ventilator settings of the controls  30  of the ventilator  20 , monitoring a plurality of output signals  51  to determine the sufficiency of ventilation support supplied to the patient P, determining the desired level settings of the controls  30  of the ventilator  20 , and controlling the level settings of the controls  30  of the ventilator  20  in response to the determined desired level settings of the controls  30  so that the ventilation support provided to the patient P coincides with the desired level settings for the controls  30 . The method may also include the step of displaying the desired level settings for the controls  30  to the operating clinician. 
     The output signals  51  may comprise a plurality of signals selected from a group of: an exhaled carbon dioxide signal indicative of the exhaled carbon dioxide (ExCO2) level of the exhaled gas expired by the patient P within the breathing circuit  22 ; a flow rate signal indicative of the flow rate (V) of the inhaled/exhaled gas inspired/expired by patient P within the breathing circuit  22 ; a pulse oximeter hemoglobin oxygen saturation (SpO2) signal indicative of the oxygen saturation level of the patient P; a pressure (P) signal indicative of the pressure of the breathing gas within the breathing circuit  22 ; a blood pressure (BP) signal indicative of the blood pressure of the patient  10 . The output signals  51  may also comprise a temperature (T) signal indicative of the core body temperature of the patient P, an arterial blood gas PaO2 signal, an arterial blood gas PaCO2 signal, and/or an arterial blood gas pH signal. 
     The ventilator setting parameter signal  42  may comprise at least one of: a minute ventilation (V E ) signal indicative of the V E  level set on the ventilator  20 ; a ventilator breathing frequency (f) signal indicative of the f level set on the ventilator  20 ; a tidal volume (V T ) signal indicative of the V T  level set on the ventilator  20 ; a breathing gas flow rate (V) signal indicative of the V level set on the ventilator  20 ; a pressure limit signal indicative of the pressure limit set on the ventilator  20 ; a work of breathing (WOB) signal indicative of the WOB level set on the ventilator  20 ; a pressure support ventilation (PSV) signal indicative of the PSV level set on the ventilator  20 ; a positive end expiratory pressure (PEEP) signal indicative of the PEEP level set on the ventilator  20 ; a continuous positive airway pressure (CPAP) signal indicative of the CPAP level set on the ventilator  20 ; and a fractional inhaled oxygen concentration (FIO2) signal indicative of the FIO2 level set on the ventilator  20 . 
     For example, the step of determining the desired level settings of the ventilator setting controls  30  may comprise the steps of generating ventilation data  72  from the received output signals  51  in the processing subsystem  40  and applying at least a portion of the generated ventilation data  72  and the ventilator setting parameter signal  42  to the neural network  82  of the processing subsystem  40 . If desired, at least a portion of the output signals  51  may also be applied to the neural network  82  as ventilation data  72 . 
     In an alternative example, the step of determining the desired level settings for the controls  30  of the ventilator  20  may comprise the steps of generating ventilation data  72  from the output signals  51  in the processing subsystem  40 , applying a set of decision rules in the rule based front-end  96  to at least a portion of the ventilation data  72  and the ventilator setting parameter signal  42  to classify the applied portions of the ventilation data  72  and the ventilator setting parameter signal  42 , selecting an appropriate neural network  82  to use, and applying a portion of the ventilation data  72  and the ventilator setting parameter signal  42  to the selected neural network  82  which will be used to determine the desired ventilation level settings of the controls  30 . 
     A realization of an embodiment of the processing subsystem  40  of the present invention is illustrated in  FIG. 7 . Here, the processing subsystem  40  includes the processor  46 , which is preferably a microprocessor, memory  48 , storage devices  64 , controllers  45  to drive the display  62 , storage  64 , and ventilator controls  30 , and an analog-to-digital converter (ADC)  47  if required. The processing subsystem  40  also includes a neural network  82 , which may, for example, be embodied in a neural network board  49 . The ADC and neural network boards  47 ,  49  are commercially-available products. There is also an optional output board (not shown) for connection to a computer network and/or central monitoring station. 
     The ADC board  47  converts the analog signal received from the output of any of the sensors  52  of the measuring means to a digital output that can be manipulated by the processor  46 . In an alternative implementation, the output of any of the sensors  52  could be connected to the processor  46  via digital outputs, e.g., a serial RS232 port. The particular implementation is determined by the output features of the particular sensor  52 . The processor  46  should contain circuits to be programmed for performing mathematical functions, such as waveform averaging, amplification, linearization, signal rejection, differentiation, integration, addition, subtraction, division and multiplication, where desired. The processor  46  may also contain circuits to be programmed for performing neural/intelligent control software, neural network learning software, and ventilator control software, as required. Circuits or programs performing these functions are conventional are well known to one skilled in the art, and they form no part of the present invention. The processor  46  executes the software which makes the computations, controls the ADC and neural network boards  47 ,  49 , and controls output to the display and storage devices  62 ,  64 , network communication, and the ventilator apparatus  20 . 
     The purpose of the neural network board  49  is to implement the neural/intelligent control software. As one skilled in the art will appreciate, the need for a separate neural network board  49  is determined by the computational power of the main processor  46 . With recent increases in microprocessor speeds, it may not be necessary to have a separate board  49 , since some or all of these functions could be handled by the processor  46 . The need for the separate board  49  is also determined by the precise platform on which the invention is implemented. 
     In addition, while the processor  46  of the processing subsystem  40  has been described as a single microprocessor, it should be understood that two or more microprocessors could be used dedicated to the individual functions. In addition, the functions of the processor  46  could be achieved by other circuits, such as application specific integrated circuits (ASIC), digital logic circuits, a microcontroller, or a digital signal processor. 
     The invention has been described herein in considerable detail, in order to comply with the Patent Statutes and to provide those skilled in the art with information needed to apply the novel principles, and to construct and use such specialized components as are required. However, it is to be understood that the invention can be carried out by specifically different equipment and devices, and that various modification, both as to equipment details and operating procedures can be effected without departing from the scope of the invention itself. Further, it should be understood that, although the present invention has been described with reference to specific details of certain embodiments thereof, it is not intended that such details should be regarded as limitations upon the scope of the invention except as and to the extent that they are included in the accompanying claims.