Abstract:
An endotracheal tube pressure monitoring system for an endotracheal tube having at least one pressure line in fluid communication with a major lumen of the endotracheal tube, a purging subsystem in fluid communication with at least one of the pressure lines, and a pressure monitoring subsystem in operative communication with each respective pressure line to monitor the pressure of fluid within each respective pressure line. Each pressure line that is in fluid communication with the purging subsystem being selectively purged by the purging subsystem when pressure monitoring subsystem determines the respective pressure line has become obstructed. Purging the pressure line maintains the patency of the pressure line so that accurate pressure measurements within the endotracheal tube can be obtained for calculation of parameters in lung mechanics. It is emphasized that this abstract is provided to comply with the rules requiring an abstract which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a system and methods used to determine pressure measurements within an endotracheal tube for use in calculation of parameters in lung mechanics and for use in determining the patency of the endotracheal tube. More specifically, the present invention is related to a system and methods for maintaining the patency of at least one pressure line in fluid communication with a major lumen of an endotracheal tube to ensure the viability of pressure measurements from the pressure line for subsequent use in calculation of parameters in lung mechanics and for use in determining the patency of the endotracheal tube, particularly for patients who are connected to a ventilator. 
     2. Background Art 
     Endotracheal pressure measurements are needed to calculate lung mechanics, for example, the calculation of work of breathing, lung compliance, and airway breathing. Such pressure measurements may also be used to assist in controlling the breathing support supplied by a ventilator, for example, the use of pressure support ventilation, demand flow ventilation and tracheal pressure control ventilation. These pressure measurements are particularly needed in patient&#39;s undergoing surgery and/or in a condition requiring connection to a ventilator. 
     Ventilators are commonly employed to assist the patient in breathing and typically include two main lines which are independently connected from the ventilator to separate branched arms from a Y-tube junction. A connector is inserted into the open stem of the Y-tube for further connection with an endotracheal tube or tracheostomy tube extending from the trachea of the patient. The main lines, the Y-tube and the connector form a breathing circuit to provide the necessary breathing support required by the condition of the patient. Airway pressure, which is the air pressure within the endotracheal tube proximate the proximal end of the endotracheal tube and may be used in such calculation of lung mechanics, is typically measured at the connection between the endotracheal tube and the breathing circuit. More particularly, it is typically measured between the endotracheal tube and the Y-tube of the breathing circuit. 
     At an appropriate pressure support ventilation level, the total work of breathing of the patient is shared between the ventilator and the patient. For the ventilator to perform a portion of the work of breathing, an appropriate level of pressure support ventilation must be preselected. To set the ventilator properly and relieve the patient&#39;s work of breathing, tracheal pressure must be accurately measured to calculate the imposed resistive work of breathing. The tracheal pressure is the air pressure within the endotracheal tube proximate the distal end of the endotracheal tube, i.e., proximate the trachea of the patient. During demand-flow spontaneous ventilation and tracheal pressure control ventilation, the patient must perform some desired portion of the work of breathing and generally must create a negative pressure to initiate a breath. Using tracheal pressure or a combination of tracheal pressure and the airway pressure measured at the connection between the endotracheal tube and the breathing circuit as the triggering pressure decreases the response time in initiating the breath and the patient&#39;s work of breathing. 
     Tracheal pressure can be measured by placing a catheter down the endotracheal tube or by using an endotracheal tube having a secondary lumen in the endotracheal tube wall, which is open at the distal end of the endotracheal tube. The catheter and the secondary lumen are subject to kinking and mucosal blockage. Tracheal pressure can be significantly lower than airway pressure and the pressure difference can change if the pressure lines that are in fluid communication with the distal and/or proximal ends of the endotracheal tube become obstructed or partially obstructed with water, or mucous, or kinked, any of which can shut off or limit the flow of fluid through the respective pressure line. Obstructions within the pressure lines may result in erroneous tracheal and/or airway pressure readings. Without the correct pressure measurements of tracheal pressure and/or airway pressure, the derived data based on the incorrect pressure measurements are predisposed to be in error, which may result in insufficient ventilation of the patient. 
     Additionally, if the endotracheal tube itself becomes obstructed with water or mucous or kinked, the flow of air delivered to the patient can be limited or shut off, which would insufficiently ventilate the lungs of the patient. Patency of the endotracheal tube may be determined by comparing the pressure of the fluid at the distal end of the endotracheal tube, i.e., the tracheal pressure, to the pressure of the fluid at the proximal end of the endotracheal tube, i.e., the airway pressure. However, the measurement of these pressures may be adversely affected by water or mucosal blockages within the respective pressure lines. 
     SUMMARY 
     The present invention relates to a pressure monitoring system for an endotracheal tube. The endotracheal tube has an open distal end, an opposing open proximal end, and a major lumen extending within the tube from the proximal end to the distal end. The distal end of the endotracheal tube is in fluid communication with a trachea of a patient. 
     The pressure monitoring system has at least one pressure line, a purging subsystem, and a pressure monitoring subsystem. Each pressure line is in fluid communication with the major lumen of the endotracheal tube. The purging subsystem is in fluid communication with at least one of the pressure lines. The pressure monitoring subsystem is in operative communication with each pressure line and has means to monitor the pressure of fluid within each respective pressure line. 
     For each pressure line in that is in fluid communication with the purging subsystem, the pressure monitoring subsystem may generate a response signal in response to a determined pressure within the pressure line which indicates that the pressure line is obstructed. In response to the response signal generated by the pressure monitoring subsystem, the purging subsystem supplies a pressurized fluid to the pressure line with which the purging subsystem is in fluid communication. This pressurized fluid clears the obstruction from the pressure line so that accurate pressure readings may be obtained from the pressure line. After a predetermined time period subsequent to the generation of the response signal, the pressure monitoring subsystem terminates the supply of the pressurized fluid to the pressure line. 
     In one embodiment, the pressure lines may include a first pressure line that is in fluid communication with the distal end of the endotracheal tube so that a tracheal pressure may be measured. Because of the high probability of blockage due to its proximity to the trachea and lungs of the patient, this first pressure line may also be in fluid communication with the purging subsystem so that the patency of the first pressure line may be maintained. Alternatively, in another embodiment, the pressure lines may include a second pressure line that is in fluid communication with the proximal end of the endotracheal tube. This second pressure line enables the measurement of airway pressure. The second pressure line may also be in fluid communication with the purging subsystem. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view of the endotracheal tube pressure monitoring system showing an endotracheal tube connected to a breathing circuit of a ventilator. 
     FIG. 2 is a schematic view of a first embodiment of the endotracheal tube pressure monitoring system showing a first pressure line in fluid communication with a distal end of an endotracheal tube and in fluid communication with a purging subsystem. 
     FIG. 3 is a schematic view of a second embodiment of the endotracheal tube pressure monitoring system showing the first pressure line in fluid communication with the distal end of the endotracheal tube and in fluid communication with the purging subsystem, and a second pressure line in fluid communication with a proximal end of the endotracheal tube. 
     FIG. 4 is a schematic view of a third embodiment of the endotracheal tube pressure monitoring system showing the first pressure line in fluid communication with a vessel of compressed fluid. 
     FIG. 5 is a schematic view of a fourth embodiment of the endotracheal tube pressure monitoring system showing the first pressure line in fluid communication with the distal end of the endotracheal tube and in fluid communication with the purging subsystem, and the second pressure line in fluid communication with a proximal end of the endotracheal tube and in fluid communication with the purging subsystem, and showing a connector attached to the proximal end of the tracheal tube for the operative connection of the second pressure line and for the insertion of a secondary lumen forming a portion of the first pressure line. 
     FIG. 6 is a schematic view of the fourth embodiment of the endotracheal tube pressure monitoring system showing the second pressure line in operable connection to a port in the connector and showing a secondary lumen in the endotracheal tube wall that forms a portion of the first pressure line. 
     FIG. 7 is a schematic view of a fifth embodiment of the endotracheal tube pressure monitoring system showing the first and second pressure lines in fluid communication with a vessel of compressed fluid. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is more particularly described in the following examples that are intended as illustrative only since numerous modifications and variations therein will be apparent to those skilled in the art. Thus, the embodiments of this invention described and illustrated herein are not intended to be exhaustive or to limit the invention to the precise form disclosed. They are chosen to describe or to best explain the principles of the invention and its application and practical use to thereby enable others skilled in the art to best utilize the invention. As used in the specification and in the claims, “a,” “an,” and “the” can mean one or more, depending upon the context in which it is used. Reference will be made to the present embodiments of the invention, whenever possible, the same reference numbers are used throughout to refer to the same or like parts. 
     Referring to FIG. 1, an endotracheal tube pressure monitoring system  10  is disclosed with an appropriately-sized endotracheal tube  20  (or tracheostomy tube) being chosen in sizes appropriate to the anatomical and physiological requirements of the patient. Any standard endotracheal tubes  20  may be used with the present invention. As one skilled in the art will appreciate, the term “endotracheal tube” is used generically to refer to any tubular conduit that may be inserted into a trachea of a patient for fluid communication with the trachea; for example, any standard endotracheal tube  20  or tracheostomy tube may be utilized. The endotracheal tube  20  has an open distal end  21 , an opposing open proximal end  22 , and a major lumen  23  extending within the tube  20  from the proximal end  22  to the distal end  21 . The endotracheal tube  20  may have a balloon cuff  25  extending around the circumference of the exterior surface of the endotracheal tube wall between the proximal and distal ends  22 ,  21 . The balloon cuff  25  may be inflated when the endotracheal tube  20  is placed into the trachea so that the trachea is sealed except for the fluid access provided by the endotracheal tube  20 . The endotracheal tube  20  generally has an attachment member  26  that forms the proximal end  22  of the endotracheal tube  20 . This attachment member  26  typically has a cylindrical attachment collar that has an outside diameter adapted to provide a frictional fit with a connector  30  of a ventilator breathing circuit. 
     Alternatively, for example, and as shown in FIGS. 1 and 6, the endotracheal tube  20  may also have a secondary lumen  56  in the endotracheal tube wall that extends at least partially along the length of the endotracheal tube  20 . The secondary lumen  56  within the tube wall has a diameter that is smaller than the diameter of the major lumen  23  of the endotracheal tube  20 . The secondary lumen  56  of this example has an opening communicating with the major lumen  23  of the endotracheal tube  20  near the distal end  21  of the endotracheal tube  20 . In this type of endotracheal tube  20 , the secondary lumen  56  typically passes through the endotracheal tube wall to the exterior of the endotracheal tube  20  at some point intermediate the proximal and distal ends  22 ,  21  of the endotracheal tube  20 . 
     As can be seen in FIG. 1, the ventilator breathing circuit also includes a Y-tube connector  40  that is frictionally fit to the connector  30  and is respectively connected to an inhalation tube  42  and an exhalation tube  44  that are, in turn, connected to a ventilator  46 . Referring to FIGS. 1-7, the connector  30  is a known type and typically has a tubular conduit  32  extending from a first end  34  to an opposing second end  36 . The connector  30  has an inside diameter sized to provide a frictional fit between the first end  34  and the Y-tube connector  40  of the ventilator breathing circuit and to provide a frictional fit between the second end  36  and the attachment member  26  (i.e., with the proximal end  22  of the endotracheal tube  20 ). The connector  30  may have one or more ports  37  that are in communication with the tubular conduit  32 . As one skilled in the art will appreciate, when the connector  30  is attached to the proximal end  22  of the endotracheal tube  20 , the ports  37  are in fluid communication with the major lumen  23  of the endotracheal tube  20 . Typically, the connector  30  has a “L”-shape in cross-section to form a right-angled connector  30 . 
     Referring generally to FIGS. 1-7, the endotracheal tube pressure monitoring system  10  of the present invention generally comprises at least one pressure line  50  in fluid communication with the major lumen  23  of the endotracheal tube  20 , a purging subsystem  80  in fluid communication with at least one pressure line  50 , and a pressure monitoring subsystem  60  in operative communication with each of the pressure lines  50  of the system  10 . 
     Each pressure line  50  is formed from one or more tubular conduits. At least a portion of each pressure line  50  is in fluid communication with the major lumen  23  of the endotracheal tube  20 . For example, a portion of the pressure line  50  may be in fluid communication with the distal end  21  of the endotracheal tube  20  so that the pressure monitoring subsystem  60  is in operative communication with the distal end  21  of the endotracheal tube  20 . In another example, a portion of the pressure line  50  may be in fluid communication with the proximal end  22  of the endotracheal tube  20  so that the pressure monitoring subsystem  60  is in operative communication with the proximal end  22  of the endotracheal tube  20 . 
     The pressure line  50 , for example, may be formed from a connector tube  58 , a secondary lumen  56 , or a connected combination of the connector tube  58  and a secondary lumen  56 . The secondary lumen  56  has a diameter smaller than the major lumen  23  of the endotracheal tube  20 . In one example, if the pressure of the fluid proximate the distal end  21  of the endotracheal tube  20  is desired to be measured, i.e., the tracheal pressure, then at least a portion of the pressure line  50  may be formed from the secondary lumen  56 , such as, for example, a catheter, extending within the endotracheal tube  20  from the distal end  21  of the endotracheal tube  20  (more particularly, the secondary lumen  56 , such as the catheter, may extend through one of the ports  37  of the connector  30  to the distal end  21  of the endotracheal tube  20 ). To communicate the fluid to the pressure monitoring subsystem  60 , the secondary lumen  56  may be connected to the pressure monitoring subsystem  60  or may be connected to the connector tube  58  which is, in turn, connected to the pressure monitoring subsystem  60 . 
     In an alternative example, if the endotracheal tube  20  has an integral secondary lumen  56  embedded within the endotracheal tube  20  side wall, as described above, then at least a portion of the pressure line  50  may comprise the integral secondary lumen  56 . To communicate the fluid within the formed pressure line  50  to the pressure monitoring subsystem  60 , the integral secondary lumen  56  of this example may be connected to the pressure monitoring subsystem  60  or may be connected to the connector tube  58  which is, in turn, connected to the pressure monitoring subsystem  60 . In yet another example, to measure the airway pressure proximate the proximal end  22  of the endotracheal tube  20 , one pressure line  50  may be connected to one of the ports  37  of the connector  30  and to the pressure monitoring subsystem  60  to communicate the fluid within the formed pressure line  50  to the pressure monitoring subsystem  60 . 
     From the examples noted above, as one skilled in the art will appreciate, the connector  30  may be used to facilitate the measurement of airway pressure proximate the proximal end  22  of the endotracheal tube  20  by allowing the connection of the pressure line  50  to a first port  38  of the connector  30 , which is adjacent the proximal end  22  of the endotracheal tube  20  and to the pressure monitoring subsystem  60 . The connector  30  may also facilitate the measurement of the tracheal pressure of the fluid proximate the distal end  21  of the endotracheal tube  20  by inserting the secondary lumen  56 , such as the catheter, through a second port  39  of the connector  30  so that the distal end of the secondary lumen  56  is proximate the distal end  21  of the endotracheal tube  20  and connecting the secondary lumen  56  to the pressure monitoring subsystem  60 . 
     The pressure monitoring subsystem  60  of the endotracheal tube pressure monitoring system  10  is in fluid communication with each pressure line  50  of the system and has a means for monitoring the pressure within each respective pressure line  50 . The pressure monitoring means includes a computing apparatus  61  and at least one pressure sensor  64 . Each pressure line  50  has a pressure sensor  64  operatively attached (i.e., disposed in the flow path of the fluid within the pressure line  50 ) for sensing the pressure of the fluid within the pressure line  50 . The pressure sensor  64  generates a pressure signal  65  representative of the pressure of the fluid proximate the pressure sensor  64 . The pressure signal  65  may be transmitted through an A/D converter (not shown) to the computing apparatus  61  on pressure signal line  66 . This pressure signal  65  may be transmitted through a digital or analog anti-aliasing filter (not shown) to remove noise above the Nyquist frequency before processing. 
     The pressure sensor  64  may be any known pressure sensor  64 , for example, a pressure transducer, a piezoresistive pressure sensor, a solid state pressure sensor, or the like. The pressure sensor  64  may, for example, use commercially available pressure sensors from Microswitch, Honeywell or Sensym. Any pressure sensor  64  capable of sensing the pressure of the fluid proximate the pressure sensor  64  and providing a signal representative of that pressure sensed could be substituted as the pressure sensor  64 . For example, an aneroid pressure manometer could be a suitable substitute. 
     The computing apparatus  61  of the pressure monitoring subsystem  60  preferably comprises a processor  62 , for example, a microprocessor, a hybrid hardware/software system, controller, computer, neural network circuit, digital signal processor, digital logic circuits, or an application specific integrated circuit (ASIC), and a memory  63 . The computing apparatus  61  is electronically coupled to each pressure sensor  64  via the pressure signal line  66 . The processor  62  of the computing apparatus  61  may be analog or digital and should contain circuits to be programed for performing mathematical functions such as, for example, waveform averaging, amplification, linearization, signal rejection, differentiation, integration, addition, subtraction, division, multiplication, and the like where desired. If an analog processor is used, the A/D converter is not required, because the analog processor requires the pressure signal to be in the non-converted analog format. 
     The parameters and data derived from the pressure signal(s)  65  produced by the pressure sensor(s)  64  are stored in the memory  63  of the computing apparatus  61  at user-defined rates, which may be continuous, for as-needed retrieval and analysis. The parameters and data may include one or more of: the pressure of the fluid within the endotracheal tube  20  proximate the distal end  21  of the endotracheal tube  20  (the tracheal pressure, P 1 ); the pressure of the fluid within the endotracheal tube  20  proximate the proximal end  22  of the endotracheal tube  20  (the airway pressure, P 2 ); the trended P 1  data; the trended P 2  data; and patency status of the endotracheal tube  20  and/or the pressure line(s)  50 . The pressure sensor(s)  64  may continually monitor/sense the pressure of the fluid proximate the respective sensor(s)  64 . The memory  63  may be, for example, a floppy disk drive, a CD drive, internal RAM, or a hard drive of the associated processor. The parameters and data may be stored to provide a permanent log of parameters and data stored that relate to the patient&#39;s course on the ventilator, and allow for on-line and retrospective analysis of the patency of the endotracheal tube  20 . As one skilled in the art will appreciate, any generated signal may be stored in the memory at user-defined rates. 
     The purging subsystem  80  of the system  10  comprises at least one source of pressurized fluid  82  that is in fluid communication with at least one pressure line  50  at a juncture  84  in the respective pressure line  50  so that a pressurized fluid may be supplied to the pressure line  50  with which it is connected. Preferably, the pressurized fluid is pressurized to at least exceed the ambient pressure of the fluid within the respective pressure line  50  so that the pressurized fluid can pass through the pressure line  50  in a direction opposite the normal flow. More preferably, the pressurized fluid is pressurized to at least exceed the pressure drop across the respective pressure line  50 . Most preferably, the pressurized fluid is pressurized to at least exceed twice the pressure drop across the respective pressure line  50 . The “opposite” flow provided by the applied pressurized fluid allows the pressurized fluid to dislodge and remove any obstructions that may be interfering with, blocking, or obstructing the normal flow of fluid through the pressure line  50 . The source of pressurized fluid  82  is responsive to the pressure monitoring subsystem  60  and may be, for example, a fluid pump  90  or a vessel of compressed fluid  92 . 
     The vessel of compressed fluid  92  may, for example be a line of compressed fluid that is typically contained in hospital room walls, such as, pressurized oxygen or air lines, or may be a self-contained vessel of pressurized fluid. The vessel of compressed fluid  92  has at least one fluid actuator  94 . The fluid actuator  94  is responsive to the pressure monitoring subsystem  60  to communicate pressurized fluid on demand to the pressure line  50  with which the vessel  92  is connected. One fluid actuator  94  is operatively connected to the respective pressure line  50  intermediate the juncture  84  and the vessel of compressed fluid  92 . Each fluid actuator  94  preferably defines a passage (not shown) through which the pressurized fluid contained in the vessel  92  traverses to reach the pressure line  50  and a fluid actuator control means for adjusting the passage to change the flow of fluid therethrough. 
     The fluid actuator control means adjusts the passage within the fluid actuator  94  in response to signals from the pressure monitoring subsystem  60 . The fluid actuator  94  is preferably a binary valve, which is in either a fully open or fully closed position. In the closed position, which is the normal operating condition, the pressurized fluid within the vessel  92  cannot communicate to its connected pressure line  50 . In the open position, which occurs during purging operations, the pressurized air from the vessel  92  is introduced into the pressure line  50  to remove obstructions from the pressure line  50 . Such a fluid actuator  94  may also be utilized in combination with the fluid pump  90  to communicate pressurized fluid on demand to the pressure line  50  with which the fluid pump  90  is connected. 
     If the pressure sensors  64  are prone to damage by the pressure of the pressurized fluid supplied by the source of pressurized fluid  82 , the purging subsystem  80  may include at least one purging actuator  96 . The purging actuator  96  preferably operates in a similar manner to the fluid actuator  94  described above. That is, one purging actuator  96  is operatively connected to the pressure line  50  intermediate the pressure sensor  64  and the juncture  84  in the pressure line  50 . Each purging actuator  96  preferably defines a passage (not shown) through which the fluid within the pressure line  50  traverses to reach the pressure sensor  64  and a purging actuator control means for adjusting the passage to change the rate of flow of the fluid therethrough. The purging actuator control means adjusts the passage within the purging actuator  96  in response to signals from the pressure monitoring subsystem  60 . Like the fluid actuator  94 , the purging actuator  96  is preferably a binary valve, which is in either a fully open or fully closed position. In the open position, which is the normal operating condition, the fluid within the respective pressure line  50  communicates with the pressure sensor  64  that is operably connected to that respective pressure line  50 . In the closed position, which is used during purging operations, fluid within the respective pressure line  50  is prevented from communicating with the pressure sensor  64 . Thus, when the purging subsystem  80  is activated, pressurized fluid is introduced into the pressure line  50  and the closed purging actuator  96  protects the connected pressure sensor  64  by preventing the introduced pressurized fluid from making contact with the pressure sensor  64 . 
     The endotracheal tube  20  pressure monitoring system  10  may further have a visual display  100  or CRT, electronically coupled to the computing apparatus  61  for outputting and displaying electronic signals generated from the computing apparatus  61 . The visual display  100  may vary the pattern of the display in accordance with the contents of the electronic output signals from the computing apparatus  61 . Preferably, the visual display  100  is a monitor but any means for displaying electronic output signals known to one skilled in the art may be used. 
     Still further, the endotracheal tube pressure monitoring system  10  may have an alarm  110  for alerting the operator of either a failure in the endotracheal tube pressure monitoring system  10 , such as a power failure, or of a patency failure or degradation of the pressure line(s)  50  or the endotracheal tube  20 . The alarm  110  may be any suitable alarm, however, preferably, the alarm  110  has a visual and/or audio alarm for alerting the operating clinician. Of course, it is desired to include a backup power supply, such as a battery. 
     The pressure monitoring subsystem  60  of the present invention is responsive to the pressure signal(s) to determine, preferably continuously, the pressure within the respective pressure line  50  and to determine, based on the determined pressure, the patency status of the respective pressure line  50 . The pressure monitoring subsystem  60  compares the trended pressure within the respective pressure line  50  over a first predetermined period of time and generates a response signal  67  based on that comparison. The preferred first predetermined period of time is the time required for the patient to complete from 2 to 10 breaths; more preferably, the first predetermined period of time is the time required for the patient to complete from 2 to 6 breaths; most preferably, first predetermined period of time is the time required for the patient to complete from 2 to 4 breaths. Typically, an adult will complete a single breath in approximately 3 second, approximately 1 second to inhale and approximately 2 seconds to exhale. 
     The pressure monitoring subsystem  60  generates the response signal  67  when the determined pressure within the respective pressure line  50  remains substantially constant for the first predetermined period of time. That is, if the determined pressure acutely freezes in place or remains substantially zero for the first predetermined period of time, the respective pressure line  50  is obstructed and the pressure monitoring subsystem  60  generates the response signal  67 . Then, in response to the response signal  67 , the alarm  110  may generate a signal that is suitable for alerting the operator that the pressure line  50  is obstructed. In a further response to the response signal  67 , if the obstructed pressure line  50  is in fluid communication with the purging subsystem  80 , the operative components of the purging subsystem  80  (as described above) are activated to purge the obstructed pressure line  50  of the obstruction. 
     When activated, the purging subsystem  80  supplies pressurized fluid to the obstructed pressure line  50  for a second predetermined period of time. Preferably, the second predetermined period of time is between approximately 0.3 to 6 seconds; more preferably is between approximately 0.3 to 4 seconds; and most preferably is between approximately 0.5 to 2 seconds. Upon the lapse of the second predetermined period of time, the purging subsystem  80  is deactivated and the components of the purging subsystem  80  are returned to their normal operative positions, which terminates supply of the pressurized fluid to the pressure line  50  with which the purging subsystem  80  is in fluid communication and allows fluid from the major lumen  23  of the endotracheal tube  20  to fluidly communicate with the pressure sensor  64 . The purging subsystem  80  may automatically be de-activated at the expiration of the second predetermined period of time. However, it is preferred that the pressure monitoring subsystem  60  generate a termination signal  68  after the second predetermined period of time lapses. Then, in response to the termination signal  68  of the pressure monitoring subsystem  60 , the purging subsystem  80  terminates supply of the pressurized fluid to the pressure line  50  with which the purging subsystem  80  is in fluid communication. As one skilled in the art will appreciate, the system  10  continuously monitors the pressure within the respective pressure line  50  and will cycle the purging subsystem  80  on and off whenever the requirements for the generation of the response signal  67  are met. For example, if an obstruction is detected in the pressure line  50 , the system  10  will continue to cycle the purging subsystem  80  until the obstruction is cleared (initially out of the affected pressure line  50  into the major lumen  23  of the endotracheal tube  20 ), by activating and de-activating the purging subsystem  80  in response to the pressure monitoring subsystem  60 . 
     When the purging subsystem  80  is activated in response to the response signal  67 , the source of pressurized fluid  82  supplies pressurized fluid to the obstructed pressure line  50  with which the purging subsystem  80  is attached. That is, if a fluid pump  90  is the source of pressurized fluid, the fluid pump  90  is activated and the fluid actuator  94 , if used, is turned to the open position to provide pressurized fluid from the fluid pump  90  to the obstructed pressure line  50 . If a purging actuator  96  is operably attached to the pressure line  50 , the purging actuator  96  is turned to the closed position so that no pressurized fluid is communicated to the pressure sensor  64  attached to the obstructed pressure line  50 . Similarly, if the vessel of compressed fluid  92  is the source of pressurized fluid  82 , the fluid actuator  94  is turned to the open position to provide pressurized fluid from the vessel  92  to the obstructed pressure line  50  and, if a purging actuator  96  is operably attached to the obstructed pressure line  50 , the purging actuator  96  is turned to the closed position so that no pressurized fluid can be communicated to the pressure sensor  64  attached to the obstructed pressure line  50 . Preferably, the fluid pump  90 , the fluid actuator  94 , the purging actuator  96  (in whatever combination used) of the purging subsystem  80  are activated and appropriately positioned substantially simultaneously. 
     In the same fashion, when the purging subsystem  80  is de-activated in response to the termination signal  68  or the lapse of the second predetermined time, the supply of pressurized fluid from the source of pressurized fluid  82  to the pressure line  50  with which the purging subsystem  80  is attached is terminated. That is, if a fluid pump  90  is the source of pressurized fluid  82 , the fluid pump  90  is deactivated and the fluid actuator  94 , if used, is turned to the closed position to terminate the supply of the pressurized fluid to the pressure line  50 . If a purging actuator  96  is operably attached to the pressure line  50 , the purging actuator  96  is turned to the open position so that fluid within the pressure line  50  may be placed in fluid communication with the pressure sensor  64  attached to the respective pressure line  50 . Similarly, if the vessel of compressed fluid  92  is the source of pressurized fluid  82 , the fluid actuator  94  is turned to the closed position to terminate the supply of the pressurized fluid to the pressure line  50  and, if a purging actuator  96  is operably attached to the obstructed pressure line  50 , the purging actuator  96  is turned to the open position so that fluid within the pressure line  50  can be communicated to the pressure sensor  64  attached to the pressure line  50 . Preferably, the fluid pump  90 , the fluid actuator  94 , the purging actuator  96  (in whatever combination used) of the purging subsystem  80  are de-activated and appropriately positioned substantially simultaneously. 
     The pressure monitoring subsystem  60  of the present invention may also be responsive to the pressure signals to determine, preferably continuously, the pressures within the respective pressure lines  50  and to determine, based on the determined pressures, the patency status of endotracheal tube  20 . In this embodiment, the pressure lines  50  include a first pressure line  52  and a second pressure line  54 . The first pressure line  52  is in fluid communication with the distal end  21  of the endotracheal tube  20  and the measured pressure within the first pressure line  52  is indicative of the tracheal pressure (P 1 ). As described above, at least a portion of the first pressure line  52  may be formed from the secondary lumen  56  or catheter. The second pressure line  54  is in fluid communication with the proximal end  22  of the endotracheal tube  20  and the measured pressure within the second pressure line  54  is indicative of the airway pressure (P 2 ). As described above, the second pressure line  54  may be connected to a port in the connector  30  to provide the necessary fluid access to the proximal end  22 . The pressure monitoring subsystem  60  compares the measured pressures and/or the trended pressures within the first and/or second pressure lines  52 ,  54  over a third predetermined period of time to determine the patency of the endotracheal tube  20 . The pressure monitoring subsystem  60  generates an output signal if the patency of the endotracheal tube  20  is determined to be degraded. In response to the output signal, the alarm  110  may be activated to alert an operator of the degraded status of the endotracheal tube  20 . Further, the output signal may be output to the visual display  100  for display to the operator of the clinical condition of the endotracheal tube  20 . 
     The preferred third predetermined period of time is the time required for the patient to complete from 2 to 10 breaths; more preferably, the first predetermined period of time is the time required for the patient to complete from 2 to 6 breaths; most preferably, first predetermined period of time is the time required for the patient to complete from 2 to 4 breaths. 
     In one example, over the third predetermined period of time, if, during the inhalation phase of ventilation, the airway pressure P 2  increases acutely and becomes significantly more positive than the trended P 1  and P 2  pressures, pressure monitoring subsystem  60  will determine that the endotracheal tube  20  is a partially obstructed. In response to this determination, the pressure monitoring subsystem  60  generates a first output signal  70  indicative of a partially obstructed endotracheal tube  20 . It is preferred that the pressure monitoring subsystem  60  generates the first output signal  70  if the airway pressure P 2  is between approximately 5-25 cm H 2 O more positive than the trended P 1  and P 2  pressures. It is more preferred that the pressure monitoring subsystem  60  generates the first output signal  70  if the airway pressure P 2  is between approximately 7-20 cm H 2 O more positive than the trended P 1  and P 2  pressures. It is most preferred that the pressure monitoring subsystem  60  generates the first output signal  70  if the airway pressure P 2  is between approximately 10-15 cm H 2 O more positive than the trended P 1  and P 2  pressures. 
     In an alternative example, over the third predetermined period of time, if during spontaneous inhalation the tracheal pressure P 1  decreases acutely and becomes more negative than the trended P 1  and P 2  data, then the pressure monitoring subsystem  60  will determine that there is increased endotracheal resistance due to a partial endotracheal tube obstruction and/or a kinked endotracheal tube  20 . In response to this determination that patency of the endotracheal tube  20  is degraded, the pressure monitoring subsystem  60  generates a second output signal  72  indicative of increased resistance within the endotracheal tube  20 . It is preferred that the pressure monitoring subsystem  60  generates the second output signal  72  if the tracheal pressure P 1  is between approximately 1-15 cm H 2 O more negative than the trended P 1  and P 2  pressures. It is more preferred that the pressure monitoring subsystem  60  generates the second output signal  72  if the tracheal pressure P 1  is between approximately 1-10 cm H 2 O more negative than the trended P 1  and P 2  pressures. It is most preferred that the pressure monitoring subsystem  60  generates the second output signal  72  if the tracheal pressure P 1  is between approximately 5-10 cm H 2 O more negative than the trended P 1  and P 2  pressures. 
     In yet another example, over the third predetermined period of time, if during spontaneous inhalation the airway pressure P 2  decreases acutely and becomes more negative than the trended P 2  data, then the pressure monitoring subsystem  60  will determine that there is increased resistance within the ventilator breathing circuit. In response to this determination, the pressure monitoring subsystem  60  generates a third output signal  74  indicative of the increased resistance within the ventilator breathing circuit. It is preferred that the pressure monitoring subsystem  60  generates the third output signal  74  if the airway pressure P 2  is between approximately 1-15 cm H 2 O more negative than the trended P 2  pressure. It is more preferred that the pressure monitoring subsystem  60  generates the third output signal  74  if the airway pressure P 2  is between approximately 1-10 cm H 2 O more negative than the trended P 2  pressure. It is most preferred that the pressure monitoring subsystem  60  generates the third output signal  74  if the airway pressure P 2  is between approximately 1-5 cm H 2 O more negative than the trended P 2  pressure. 
     Referring now to FIG. 2, a first embodiment of an exemplified endotracheal tube pressure monitoring system  10  is shown. Here, the endotracheal tube  20  is connected to the connector  30  which is, in turn, connected to the ventilator. The endotracheal tube  20  is inserted into the trachea of the patient so that the distal end  21  of the endotracheal tube  20  is placed in fluid communication with the trachea of the patient. 
     The endotracheal tube pressure monitoring system  10  is shown with one pressure line  50 . This pressure line  50  is in fluid communication with the distal end  21  of the endotracheal tube  20 . Because of the likelihood that the pressure line  50  used in this embodiment will become obstructed due to water or mucus plugs (due to pressure line&#39;s  50  proximity to the body fluids in and around the trachea), this example of the system is shown with the pressure line  50  in fluid communication with the purging subsystem  80 . The purging subsystem  80  is shown with the source of pressurized fluid  82 , for example here a fluid pump  90 , in communication with the pressure line  50  at a juncture  84  in the pressure line  50 . 
     The purging actuator  96  is intermediate the juncture  84  and the pressure sensor  64  of the pressure monitoring subsystem  60 . Thus, in this example, the tracheal pressure may be monitored and the pressure line  50  may be maintained free from obstructions by activating and deactivating the purging subsystem  80  in response to the response and termination signals  67 ,  68  generated by the pressure monitoring subsystem  60 . 
     Referring now to FIG. 3, a second embodiment of an exemplified endotracheal tube pressure monitoring system  10  is shown. In this embodiment, the system has a first pressure tube in fluid communication with the distal end  21  of the endotracheal tube  20  and a second pressure tube connected to a port of the connector  30  and in fluid communication with the proximal end  22  of the endotracheal tube  20 . Airway pressure may be determined by the fluid within the first pressure line  52  communicating with a first pressure sensor  64  operably attached to the first pressure line  52 . Similarly, tracheal pressure may be determined by the fluid within the second pressure line  54  which, is in communication with a second pressure sensor  64  operably attached to the second pressure line  54 . 
     The purging subsystem  80 , which includes here, for example, one fluid pump  90 , and the first purging actuator  96 , is in fluid communication with the first pressure line  52  so that the first pressure line  52  may be maintained free from obstructions by activating and deactivating the purging subsystem  80  in response to a first response signal  67  and a first termination signal  68  generated by the pressure monitoring subsystem  60 . The fluid pump  90  is responsive to the first response signal  67  to supply the pressurized fluid to the first pressure line  52  and the first purging actuator  96  is responsive to the first response signal  67  to move to the closed position so that fluid is prevented from being communicated to the first pressure sensor  64 . The fluid pump  90  is responsive to the first termination signal  68  to terminated supply of the pressurized fluid to the first pressure line  52  and the first purging actuator  96  is responsive to the first termination signal  68  to move to the open position so that fluid within the first pressure line  52  is in fluid communication with the first pressure sensor  64 . 
     Turning now to the third embodiment of an exemplified endotracheal tube pressure monitoring system  10  shown in FIG. 4, the second embodiment described above is shown with the source of pressurized fluid  82  being the vessel of compressed fluid  92  having a fluid actuator  94 . Here, the fluid actuator  94  of the vessel  92  is responsive to the first response signal  67  to supply the pressurized fluid to the first pressure line  52  by moving to the open position in which pressurized fluid is communicated from the vessel  92  to the first pressure line  52 . Additionally, the first purging actuator  96  is responsive to the first response signal  67  to move to the closed position so that fluid is prevented from being communicated to the first pressure sensor  64 . The fluid actuator  94  is responsive to the first termination signal  68  to terminate supply of the pressurized fluid from the vessel  92  to the first pressure line  52  by moving to the closed position in which pressurized fluid from the vessel  92  is not communicated from the vessel  92  to the first pressure line  52 . Also, the first purging actuator  96  is responsive to the first termination signal  68  to move to the open position so that fluid within the first pressure line  52  is communicated to the first pressure sensor  64 . 
     Referring to FIG. 5, a fourth embodiment of the endotracheal tube pressure monitoring system  10  is shown. In this embodiment, the system has a first pressure tube in fluid communication with the distal end  21  of the endotracheal tube  20  and a second pressure tube connected to a port of the connector  30  and in fluid communication with the proximal end  22  of the endotracheal tube  20 . The airway pressure may be determined by the fluid within the first pressure line  52  communicating with a first pressure sensor  64  operably attached to the first pressure line  52 . Similarly, tracheal pressure may be determined by the fluid within the second pressure line  54 , which is in communication with a second pressure sensor  64  operably attached to the second pressure line  54 . 
     Here, for example, the purging subsystem  80  includes two fluid pumps  90  and two purging actuators  96 . The first fluid pump  90  in fluid communication with the first pressure line  52  and the second fluid pump  90  in fluid communication with the second pressure line  54  and the first and second purging actuators  96  are in fluid communication with the respective first and second pressure lines  52 ,  54  so that the first and second pressure lines  52 ,  54  may be maintained free from obstructions. By activating and deactivating the purging subsystem  80  in response to the respective first and second response signals  67  and the respective first and second termination signals  67 ,  68  generated by the pressure monitoring subsystem  60  when an obstruction is detected in the respective pressure lines. As one skilled in the art will appreciate, the pressure monitoring subsystem  60  will generate the response signal  67  and termination signal  68  for the respective pressure line  52 ,  54  when the appropriate conditions are met. 
     The first fluid pump  90  is responsive to the first response signal  67  to supply the pressurized fluid to the first pressure line  52  and the first purging actuator  96  is responsive to the first response signal  67  to move to the closed position so that fluid is prevented from being communicated to the first pressure sensor  64 . In like fashion, the second fluid pump  90  is responsive to the second response signal  67  to supply the pressurized fluid to the second pressure line  54  and the second purging actuator  96  is responsive to the second response signal  67  to move to the closed position so that fluid is prevented from being communicated to the second pressure sensor  64 . As one skilled in the art will appreciate, the first fluid pump  90  is responsive to the first termination signal  68  to terminated supply of the pressurized fluid to the first pressure line  52  and the first purging actuator  96  is responsive to the first termination signal  68  to move to the open position so that fluid within the first pressure line  52  is in fluid communication with the first pressure sensor  64 . In response to the second termination signal  68 , the second purging actuator  96  moves to the open position so that fluid within the second pressure line  54  is in fluid communication with the second pressure sensor  64  and the second fluid pump  90  terminates supply of the pressurized fluid to the second pressure line  54 . 
     Referring now to FIG. 6, the fourth embodiment described above and shown in FIG. 5, is illustrated connected to an endotracheal tube  20  having a secondary lumen  56  in the endotracheal tube wall. Here, the second pressure line  54  is shown in operable connection with a port of the connector  30  and in fluid communication with the proximal end  22  of the endotracheal tube  20  for the measurement of the airway pressure. A portion of the first pressure line  52  is formed from the secondary lumen  56  in the endotracheal tube wall, which is in fluid communication with the distal end  21  of the endotracheal tube  20  and the remaining portion of the first pressure line  52  is formed by the connection of the connector tube  58 . 
     The fifth embodiment of the exemplified endotracheal tube pressure monitoring system  10  shown in FIG. 7, is different from the fourth embodiment described above and illustrated in FIG. 5 because the source of pressurized fluid  82  shown is the vessel of compressed fluid  92  having a plurality of fluid actuators  92 . Here, for example, the fluid actuators  92  include a first fluid actuator  94  and a second fluid actuator  94 . The first fluid actuator  94  of the vessel  92  is responsive to the first response signal  67  to supply the pressurized fluid to the first pressure line  52  by moving to the open position in which pressurized fluid is communicated from the vessel  92  to the first pressure line  52 . In a similar fashion, the second fluid actuator  94  of the vessel  92  is responsive to the second response signal  67  to supply the pressurized fluid to the second pressure line  54  by moving to the open position in which pressurized fluid is communicated from the vessel  92  to the second pressure line  54 . 
     Still referring to FIG. 7, to protect the potentially fragile first and second pressure sensors  64 , the first and second purging actuators  96  are responsive to the respective first and second response signals  67  to move to the closed position so that pressurized fluid being supplied to the respective first and second pressure lines  52 ,  54  is prevented from being communicated to the respective first and second pressure sensors  64 . 
     The first fluid actuator  94  is responsive to the first termination signal  68  to terminate supply of the pressurized fluid from the vessel  92  to the first pressure line  52  by moving to the closed position, in which pressurized fluid from the vessel  92  is not communicated from the vessel  92  to the first pressure line  52 . At substantially the same time, the first purging actuator  96  is responsive to the first termination signal  68  to move to the open position so that fluid within the first pressure line  52  is communicated to the first pressure sensor  64 . For the second pressure line  54 , the second fluid actuator  94  is responsive to the second termination signal  68  to terminate supply of the pressurized fluid from the vessel  92  to the second pressure line  54 . The second fluid actuator  94  is moved to the closed position in which pressurized fluid from the vessel  92  may not be communicated from the vessel  92  to the second pressure line  54 . At substantially the same time, the second purging actuator  96  is responsive to the second termination signal  68  to move to the open position so that fluid within the second pressure line  54  is communicated to the second pressure sensor  64 . 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.