Patent Publication Number: US-6910479-B1

Title: Airway treatment apparatus with bias line cancellation

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     Reference is made to the following applications which are filed on even date and assigned to the same assignee as this application: AIRWAY TREATMENT APPARATUS WITH AIRFLOW ENHANCEMENT, Ser. No. 09/412,768, now U.S. Pat. No. 6,340,025; AIRWAY TREATMENT APPARATUS WITH COUGH INDUCEMENT, Ser. No. 09/412,457, now U.S. Pat. No. 6,415,791; and OUTCOME MEASURING AIRWAY RESISTANCE DIAGNOSTIC SYSTEM, Ser. No. 09/412,086, now U.S. Pat. No. 6,210,345. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to an airway clearance system and in particular to a system that includes a chest compression device for high frequency chest wall oscillation and a subsystem which cancels bias line pressure and enhances airflow velocity through the air passages caused by the high frequency chest wall oscillations. 
     Chest compression devices have been developed to produce high frequency chest wall oscillation (HFCWO). HFCWO is the most successful method used for removing excess mucus from the lungs caused by a variety of diseases such as cystic fibrosis, emphysema, asthma, chronic obstructive pulmonary disease (COPD), and chronic bronchitis. 
     The device most widely used to produce HFCWO is the ABI Vest™ Airway Clearance System by American Biosystems, the assignee of the present application. A description of the pneumatically driven system can be found in the Van Brunt et al. patent, U.S. Pat. No. 5,769,797, which is assigned to American Biosystems. Another example of a pneumatic chest compression vest has been described by Warwick et al., U.S. Pat. No. 4,838,263. 
     Pneumatically driven HFCWO produces substantial transient increases in the airflow velocity with a small displacement of the chest cavity volume. This action produces a cough-like shear force and reduction in mucus viscosity that results in an upward motion of the mucus. The ABI Vest Airway Clearance System is effective in clearing. airways of mucus, however, there are limitations of its performance. 
     There is a constant vest pressure on the chest of the patient when using the vest. This can cause particular problems with some disease states. External pressure on the chest of a COPD patient during inspiration may cause considerable distress. Also, asthmatics may find the constant vest pressure extremely irritating, and those with constricted and inflamed airways may find it uncomfortable. Therefore, eliminating the constant vest pressure would be beneficial. 
     It is difficult to determine a short term reduction in airway resistance during treatment. Airway resistance is the ratio of airway pressure to airway airflow. It is an indicator of the degree of plugging of the lung passages by mucus, and therefore, periodic measurement of airway resistance provides a good indicator - of the success or lack thereof of a treatment for lung clearance. 
     Prior art vest systems do not have the ability to aid in removing mucus from the upper airway passages. With some disease states, the debilitated patient is unable to produce a cough to remove the mucus accumulated in the upper airway passages. Normally, the current vest systems accelerate the mucus upward and outward in the upper bronchial passages and trachea by increasing airflow velocity. Many individuals can then, by means of a volitional cough, force the mucus into the mouth and then expectorate. The effectiveness of the treatment is greatly reduced if a weakened individual is unable to do this. Also, since a cough is an effective natural method of moving the mucus out of the airway, it would be beneficial to have a system which produced a cough on each oscillation of the chest wall. 
     Since increased airflow velocity is key to clearing the lungs of mucus, it would be advantageous to improve upon the current systems in order to induce even higher airflow velocities from users. This would make the vest system even more effective at removing mucus from the lungs. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention is a method and apparatus for clearing a patient&#39;s lungs of mucus. An oscillating compressive force is applied to the patient&#39;s chest that includes a steady state force component and an oscillating force component. Air pressure is supplied to the patient&#39;s mouth via a mouthpiece to at least partially cancel the steady state force component. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a block diagram of a first embodiment which provides enhanced airway flow and chest compression bias line cancellation. 
         FIG. 2  is a block diagram of a second embodiment of an airway treatment apparatus which includes simulated cough inducement. 
         FIG. 3  is a schematic block diagram of the cough waveform generator module of  FIG. 2 . 
         FIG. 4   a  shows one oscillation of the chest wall force applicator pressure and airflow velocity during a simulated cough sequence. 
         FIG. 4   b  shows multiple oscillations of the chest wall force applicator pressure and airflow velocity during simulated cough sequences. 
         FIG. 5  is a block diagram of a third embodiment of an airway treatment apparatus which provides airway resistance measurement. 
         FIG. 6  is a schematic block diagram of the airway resistance module of  FIG. 5 . 
         FIG. 7  is a schematic block diagram of the airway resistance null detector/indicator module of FIG  5 . 
         FIG. 8   a  is a graph of pressure waves during chest compression treatment from a chest wall force applicator and at a mouthpiece when the pressure at the mouthpiece is less than pressure produced by the chest wall force applicator. 
         FIG. 8   b  is a graph of pressure waves during chest compression treatment from the chest wall force applicator and at the mouthpiece when the pressure at the mouthpiece is at null. 
         FIG. 8   c  is a graph of pressure waves during chest compression treatment from the chest wall force applicator and at the mouthpiece when pressure at the mouthpiece is greater than pressure produced by the chest wall force applicator. 
         FIG. 9  is a block diagram of a fourth embodiment of an airway treatment apparatus which includes all of the features of the first, second, and third embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     FIRST EMBODIMENT (FIG.  1 ) 
       FIG. 1  is a block diagram showing a patient P undergoing treatment using the preferred embodiment of airway treatment apparatus  10 . As shown in  FIG. 1 , apparatus  10  has two major subsystems, chest wall force applicator  12   a  (which applies oscillating compressive force to the chest of patient P) and air pressure input mouthpiece system  12   b  (which supplies air pressure to the patient&#39;s mouth in a relationship to the compressive force). 
     Chest wall force applicator  12   a  includes brushless motor  14 , vest oscillation frequency potentiometer  16 , motor controller  18 , shaft  20 , wheel  22 , reciprocating arm  24 , pin  26 , diaphragm  28 , air chamber  30 , blower  32 , vest pressure potentiometer  34 , blower controller  36 , tube  38   a  with constriction  38   b , hoses  40 , and inflatable vest  42 . Oscillated air pressure is delivered to inflatable vest  42  to cause inflatable vest  42  to apply an oscillating force to the patient&#39;s chest. 
     Brushless motor  14  is operated by motor controller  18  at a speed which is set by vest oscillation frequency potentiometer  16 . Shaft  20  is connected to brushless motor  14  and wheel  22 . Reciprocating arm  24  is coupled to wheel  22  by pin  26 , which is offset from the center of wheel  22 . Reciprocating arm  24  is also coupled to diaphragm  28 , which is part of air chamber  30 . 
     Blower  32  is operated by blower controller  36  based upon a control setting of potentiometer  34 . Tube  38   a  with constriction  38   b  couples blower  32  with air chamber  30 . Hoses  40 , in turn, couple air chamber  30  with inflatable vest  42 . 
     The force generated on the patient&#39;s chest by chest wall force applicator  12   a  has an oscillatory air pressure component and a steady state air pressure component. In a preferred embodiment, the steady state air pressure (or “bias line pressure”) is greater than atmospheric pressure, and the oscillatory air pressure rides on the steady state air pressure. With this embodiment, a whole oscillation of chest wall force applicator  12   a  is effective at moving the patient&#39;s chest, because there is no point at which pressure applied to the chest by vest  42  is below atmospheric pressure. Chest movement can only be induced while chest wall applicator  12   a  has an-effective pressure (i.e. greater than atmospheric pressure) on the patient&#39;s chest. 
     The oscillatory air pressure component is created by brushless motor  14 . The speed of brushless motor  14  is selected by vest oscillation potentiometer  16  and held constant by motor controller  18 . Shaft  20  of brushless motor  14  rotates wheel  22  which, in turn, moves reciprocating arm  24  in a linear fashion and causes diaphragm  28  to oscillate the air in air chamber  30  at a frequency selected by vest oscillation potentiometer  16 . The pressure created by brushless motor  14  follows a sinusoidal waveform pattern. 
     To create the steady state air pressure, vest pressure potentiometer  34  selects the speed of blower  32  and the speed is held constant by blower controller  36 . The steady state air pressure is transferred to air chamber  30  through tube  38   a . Constriction  38   b  within tube  38   a  prevents backflow of pressure pulses into blower  32  which would affect the pressure pulsation in a nonlinear manner. In effect, constriction  38   b  is a large impedance to oscillatory airflow but a low impedance to steady state airflow. The steady state air pressure created by blower  32  is greater than atmospheric pressure so that a whole oscillatory cycle is effective at moving the patient&#39;s chest. Preferably, blower  32  has a pressure maximum of 12 cm of water, which is well within tolerance limits of anticipated users. This is a safety feature designed so that if any component failure tended to speed up blower  32 , it would not be unsafe. 
     Hoses  40  convey air pressure waves from air chamber  30  to inflatable vest  42 . Inflatable vest  42 , thus, is cyclically inflated and deflated to apply HFCWO to the patient&#39;s chest at a frequency set by vest oscillation frequency potentiometer  16  about a steady state or bias line pressure set by vest pressure potentiometer  34 : The steady state air pressure determines the intensity of the chest compressions since the oscillatory air pressure rides on the steady state air pressure. Therefore, the change of pressure (delta pressure) increases with increasing steady state pressure and results in the oscillatory air pressure never being less than atmospheric pressure. In applying HFCWO to the patient&#39;s chest, the patient&#39;s airways are cleared of ran mucus. 
     Chest wall force applicator  12   a  also includes components to link it to air pressure input mouthpiece system  12   b . These include vest sampling tube  50 , vest pressure transducer (VPT)  52 , phase shift network  54 , line  56 , line  58 , and Oscillatory Positive Expiratory Pressure (OPEP) oscillation intensity potentiometer  60 . 
     Vest sampling tube  50  is connected to inflatable vest  42  at one end and vest pressure transducer  52  at the other end. Vest pressure transducer  52  is connected to phase shift network  54  via line  56 . Line  58  then connects phase shift network  54  to OPEP potentiometer  60 . 
     In operation, vest sampling tube  50  conveys vest pressure to vest pressure transducer  52  which converts it to an electrical signal representative of sensed vest pressure. The electrical output signal of vest pressure transducer  52  is sent to phase shift network  54  via line  56 . Phase shift network  54  compensates for delays in oscillatory pressure from chest wall force applicator  12   a  being transmitted as an oscillation within the patient&#39;s lungs and to the patient&#39;s mouth. The signal from phase shift network  54  (having a waveform representative of vest pressure applied by chest wall force applicator  12   a ) is supplied by line  58  to OPEP potentiometer  60  and then to air pressure input mouthpiece system  12   b . 
     Air pressure input mouthpiece system  12   b  includes motor drive amplifier  72 , line  74 , summing junction  76 , line  78 , diaphragm  80 , linear motor  82 , air chamber  84 , sampling tube  86 , pressure transducer(PT)  88 , line  90 , low pass filter (LPF)  92 , comparator error amplifier  94 , line  96 , line  98 , Positive Expiratory Pressure (PEP) level potentiometer  100 , line  102 , blower controller motor driver  104 , blower  106 , tube  108   a  with constriction  108   b , tube  110 , and mouthpiece  112  (with mouth port  112   a , air supply port  112   b , and outlet port  114 ). 
     Wiper  60   a  of OPEP potentiometer  60  is connected to motor drive amplifier  72  via line  74 , summing junction  76 , and line  78 . Motor drive amplifier  72  is connected to diaphragm  80  of linear motor  82 . Diaphragm  80  is then connected with air chamber  84  which is coupled to sampling tube  86  followed by pressure transducer  88 . Line  90  connects pressure transducer  88  to low pass filter  92  which is followed by a connection to summing junction  76  and to comparator error amplifier  94  via lines  96  and  98 . Comparator error amplifier  94  is also connected to PEP level potentiometer  100  through line  102  and to blower controller motor driver  104 . Blower controller motor driver  104  provides a drive signal to blower  106 , which is coupled to air chamber  84  by tube  108   a  that contains constriction  108   b . Tube  110  extends from air chamber  84  and connects to air supply port  112   b  of mouthpiece  112 . Mouth port  112   a  of mouthpiece  112  is placed in communication with the patient&#39;s mouth (i.e. either in or over the mouth). Mouthpiece  112  may also cover the patient&#39;s nose. Outlet port  114  is located a short distance from mouthpiece  112  on tube  110 . 
     In operation, the processed pressure waveform from vest pressure transducer  52  and phase shift network  54  is input to OPEP potentiometer  60  as described above. OPEP potentiometer  60  adjusts an Oscillatory Positive Expiratory Pressure (OPEP) intensity level to control the amount of airflow enhancement at the patient&#39;s mouth that is input to motor drive amplifier  72 . Based upon a control signal from summing junction  76 , motor drive amplifier  72  operates linear motor  82  causing diaphragm  80  of linear motor  82  to oscillate air within air chamber  84 . The control signal is based upon the PEP feedback signal from low pass filter  92  (which represents the steady state pressure in chamber  84 ) and the signal waveform from phase shift network  54  through OPEP potentiometer  60 . The oscillatory waveform. created in air chamber  84  is selected with the desired phase, intensity, and wave shape to perform the needed task. Linear motor  82  is not restricted to a sinusoidal. waveform and can move in any complex pattern. Other embodiments of the invention may use other components to produce the same waveforms as linear motor  82  such as a solenoid or a motor driven cam mechanism. 
     Air pressure from air chamber  84  is measured by sampling tube  86  and pressure transducer  88  relative to atmospheric pressure. The electrical signal generated by pressure transducer  88  is filtered by low pass filter  92 , which has such a low frequency cutoff that the output from low pass filter  92  is essentially the average pressure in air chamber  84  produced by filtering out the effects of linear motor  82  and then carried on line  96 . This PEP feedback signal is carried to the minus (−) input of comparator error amplifier  94  by line  98 . PEP level potentiometer 100 selects a Positive Expiratory Pressure (PEP) level which is fed into the plus (+) input of comparator error amplifier  94  via line  102 . The PEP level is adjusted by PEP level potentiometer 100 to match the mean pressure exerted on the patient&#39;s chest wall by chest wall force applicator  12   a . The output of comparator error amplifier  94  activates blower controller motor driver  104  which maintains the speed of blower  106 . Since blower  106  communicates with air chamber  84  through tube  108   a , the steady state pressure bias is regulated within air chamber  84 . Constriction  108   b , within tube  108   a , prevents back flow of pressure pulses to blower  106  which would effect the pressure pulsation as previously discussed. The steady state pressure bias is maintained in the patient&#39;s mouth through communication with air chamber  84  via tube  110  and mouthpiece  112 . 
     Air pressure input mouthpiece system  12   b  accomplishes, in effect, a shift in the effective atmospheric pressure. An oscillatory airflow is produced that rides on a steady state pressure (which is greater than atmospheric pressure) in the mouth. The combined oscillatory pressure and steady state pressure has a waveform, intensity and phase relationship to the chest compressions that enhances airflow through the air passages. In addition, the patient perceives no vest pressure, because the steady state pressure in the mouth and lungs is equal to and opposite the pressure from chest wall force applicator  12   a , and thus, the forces counteract each other. This is very beneficial with some disease states where the external pressure on the chest from a chest wall force applicator  12   a  can cause considerable distress to the patient. A patient may already have difficulty breathing and would have even greater difficultly if the patient had to breathe against a force trying to compress the patient&#39;s lungs. 
     Air pressure input mouthpiece system  12   b  also provides an effective means of enhancing oscillations caused by chest wall force applicator  12   a  without increasing the force applied on the patient&#39;s chest. Increased force on the patient&#39;s chest would be too uncomfortable. Therefore, air pressure input mouthpiece system  12   b  enhances the function of chest wall force applicator  12   a  by oscillating the pressure at the patient&#39;s mouth in synchronism with the airflow produced by the oscillations on the chest by chit walt force applicator  12   a . 
     Since OPEP potentiometer  60  regulates the extent to which air pressure input mouthpiece system  12   b  enhances airflow velocity created by chest wall force applicator  12   a , it can alternatively be set to (a) increase the volume of the lungs slightly by increasing the pressure in air chamber  84  or (b) deflate the lungs by decreasing the pressure in air chamber  84 . This is a beneficial function, because in some disease states the lungs need to be given greater volume. In other disease states where the lungs may be hyperinflated, it is desirable to reduce the lungs&#39; volume. 
     Outlet port  114  is located a short distance from mouthpiece  112 . The distance is determined by the distance 100% humidified air from mouthpiece  112  travels in one cycle. This allows the humid air from the outflow half cycles to be returned to the patient&#39;s airways during the inflow half cycles, thus preventing the airways from drying out. The positive pressure produced by blower  106  maintains a net average of airflow from blower  106  through air chamber  84  and tube  110  and out outlet port  114 . Therefore, any fluids and mucus are drained out through outlet port  114  and not passed into air chamber  84  where they could cause damage. In addition, this airflow stream provides a continuous supply of fresh air for normal respiration as the much larger tidal breathing volume oscillations move fresh air from the position of outlet port  114  in tube  110  into the patient&#39;s lungs. 
     SECOND EMBODIMENT (FIGS.  2 – 4 B) 
       FIG. 2  shows a second embodiment of apparatus  10 , having a simulated cough inducer  12   c , which includes cough waveform generator module  160  and light interrupter  164 . The embodiment shown in  FIG. 2  is generally similar to the embodiment of  FIG. 1 , and similar reference characters are used to designate similar elements.  FIG. 3  shows a schematic block diagram of cough waveform generator module  160 , which includes optical sensor processor  166 , cough waveform generator  168 , line  170 , cough intensity potentiometer  172 , line  174 , and summing junction  176 . 
     Light interrupter  164  ( FIG. 2 ) is attached to wheel  22  and sends signals to optical sensor processor  166 . These components make up a diaphragm position sensor which is connected to cough waveform generator  168  via line  170 . The output of cough waveform generator  168  is connected to Cough Intensity potentiometer  172 . Line  174  connects Cough Intensity potentiometer  172  with one input of summing junction  176 . Another input of summing junction  176  is connected to wiper  60   a  of OPEP potentiometer  60 . Line  74  connects the output of summing junction  176  with an input of summing junction  76 . The output of summing junction  76  is connected to motor drive amplifier  72  through line  78 . 
     In operation, the diaphragm position sensor formed by light interrupter  164  and optical sensor processor  166  produces a timing signal that..... triggers the start and finish of cough waveform generator  168 . When oscillatory lung pressure peaks (as indicated by the position of light interrupter  164 ), optical sensor processor  166  activates cough waveform generator  168 . Optical sensor processor  166  stops cough waveform generator  168  when oscillatory lung pressure a reaches zero (as indicated by the position of light interrupter  164 ). Cough Intensity potentiometer  172  determines the magnitude of the signal from cough waveform generator  168 , and the signal is carried to summing junction  176  via line  174 . As described previously, OPEP potentiometer  60  sets the level of the OPEP waveform, and this signal is also supplied to sunning junction  176 . Summing junction  176  then combines the OPEP waveform signal with the cough waveform signal from cough waveform generator  168 . The output of summing junction  176 , which includes the cough waveform set at the desired intensity, is carried through line  74  to summing junction  76 . The combined OPEP/cough signal is summed with the steady state pressure signal from low pass filter  92  and is sent to motor drive amplifier  72  along line  78 . 
     During one phase of the cough sequence, the pressure wave from air chamber  84  causes near zero airflow out of mouthpiece  112 . Simultaneously, pressure from chest wall force applicator  12   a  on the chest is increasing. What results is a build up of airway pressure in the lungs with very little outward flow. In the next phase, approximately when lung pressure peaks, there is a rapid increase in the flow outward from the lungs. Therefore, the flow rate while inspiring is lower than the flow rate while expiring, but the volume of air during each half cycle is equal. Since this is the pattern of a natural cough, a cough is simulated with each oscillatory cycle, which can be up to 20 times/second. 
     In one embodiment, simulated cough inducer  12   c  can be utilized instead of enhancing the increased airflow velocities created by chest wall force applicator  12   a  using sinusoidal enhancement with air pressure input mouthpiece system  12   b . In another embodiment, OPEP potentiometer  60  (which adjusts the magnitude of sinusoidal enhancement) and Cough Intensity potentiometer  172  (which controls the magnitude of the cough waveform) can be combined in any proportion at summing junction  176  to provide the desired effect. 
       FIGS. 4   a  and  4   b  illustrate the cough sequence.  FIGS. 4   a  and  4   b  show pressure from chest wall force applicator  12   a  on the patient&#39;s chest and airflow from the patient&#39;s mouth during a cough sequence.  FIG. 4   a  shows one oscillatory cycle and  FIG. 4   b  shows multiple oscillatory cycles. The sinusoidal wave is a vest pressure waveform  180  and the jagged waveform  182  is airflow at the patient&#39;s mouth. The high frequency oscillations of the airflow waveform are caused by resonance of the tubes within the present invention and the patient&#39;s air passages and are of no consequence. 
     Line  184 , of  FIG. 4   a , indicates zero airflow. When the waveform is above this line, the patient is inspiring and when below the line, the patient is expiring. Vest pressure increases downward from line  186 . Prior to about point  188 , airflow is about zero. This is the period of building pressure in the lungs and is equivalent to the glottis closing during a natural cough in order to allow pressure to build in the lungs. At about point  188 , vest pressure peaks, and airflow from the mouth is at a maximum. This coincides with the rapid increase in airflow out of the mouth when the glottis opens during a natural cough. Expiratory rate is up to 3 liters/second. Point  190  shows a gradual inspiration, as in a natural cough. Integration of the airflow waveform  182  below and above line  184  produces a net flow of zero.  FIG. 4   b  shows the cough sequence at a different time scale illustrating multiple induced coughs. 
     With the present invention, even weakened individuals that cannot voluntarily cough can clear mucus from upper bronchial passages and trachea into the mouth to expectorate the mucus. Even for individuals with normal strength, coughing is an effective way of cleaning mucus from airways, and therefore, this greatly enhances the mucus clearing capability of the invention. 
     THIRD EMBODIMENT (FIGS.  5 – 8 C) 
       FIG. 5  shows a third embodiment of apparatus  10  which further includes airway resistance indicator  12   d . The embodiment shown in  FIG. 5  is generally similar to the embodiment shown in  FIG. 1 , and similar reference characters are used to designate similar elements. Airway resistance indicator  12   d  includes airway resistance module  200  (shown in  FIG. 6 ), airway resistance null. detector/indicator module  210  (shown in  FIG. 7 ) and test switch  220  (having terminals  220   a – 220   c ). 
     Airway resistance module  200  ( FIG. 6 ) includes vest pressure transducer  52 , phase shift network  54 , lines  56  and  58 , and PFT potentiometer  230 , and lines  232  and  234 . Vest pressure transducer  52  is linked to inflatable vest  42  by vest sampling tube  50 . Phase shift network  54  is coupled to vest pressure transducer  52  via line  56 . Line  58  connects phase shift network  54  with PFT potentiometer  230 , which is connected to terminal  220   a  of test switch  220  by line  232 . Line  234  couples the output of vest pressure transducer  52  with airway resistance null detector/indicator  210 . 
     Airway resistance null detector/indicator module  210  ( FIG. 7 ) includes pressure tube  240 , pressure transducer  242 , line  244 , capacitor  246 , double pole switch  248 , line  250 , phase shift network  252 , line  254 , integrator  256  with integrator capacitor  258 , level indicator  260 , and LEDs  262  and  264 . Pressure tube  240  is coupled to mouthpiece  112  and pressure transducer  242 . Through line  244 , the output of pressure transducer  242  is connected to capacitor  246  which is connected to double pole switch  248  via line  250 . Double pole switch  248  has one output terminal connected to integrator  256  with integrator capacitor  258 , and the other output terminal connected to ground. The input of level indicator  260  is connected to integrator  256 , and the output of level indicator  260  is connected with and selectively drives LEDs  262  and  264 . Signals from airway resistance module  200  are carried to phase shift network  252  which is connected to the control input of double pole switch  248  via line  254 . 
     In operation, vest sampling tube  50  conveys vest pressure to vest pressure transducer  52  ( FIG. 6 ) which converts it to an electrical signal. The electrical output signal of vest pressure transducer  52  is sent to phase shift network  54  via line  56 . Phase shift network  54  compensates for delays in oscillatory pressure from chest wall force applicator  12   a  being transmitted as an oscillation within the patient&#39;s lungs and to the patient&#39;s mouth. The signal from phase shift network  54  (having a waveform representative of vest pressure applied by chest wall force applicator  12   a ) is subsequently carried by line  58  to PFT potentiometer  230  (as well as to OPEP potentiometer  60 ). 
     At the same time, pressure tube  240  samples the pressure in the patient&#39;s mouth. Transducer  242  ( FIG. 7 ) converts this pressure to an electrical signal. The output of transducer  242  is carried to capacitor  246  via line  244 . Line  250  then carries the signal from capacitor  250  to the input of double pole switch  248 . Capacitor  246  removes the dc signal component from the electrical output signal of pressure transducer  242 . 
     A vest pressure signal is a control input into double pole switch  248 . Line  234  inputs the vest pressure signal from vest pressure transducer  52  ( FIG. 6 ) to phase shift network  252 , which controls the switch timing of double pole switch  248 . The signal from phase shift network  252  is carried to double pole switch  248  through line  254  and switches to ground to discharge any accumulated charge on capacitor  246 , which prevents a dc voltage build up. 
     When the compressive force of vest  42  of chest wall applicator  12   a  peaks, double pole switch  248  connects capacitor  246  to the input of integrator  256  to sample the mouth pressure waveform fed through capacitor  246 . If the average signal output of integrator  256  indicates that the oscillatory pressure in mouthpiece  112  is less than the lung oscillatory pressure, level indicator  260  lights LED  262 .. If the average signal output of integrator  256  indicates that the oscillatory pressure in mouthpiece  112  is greater than the lung oscillatory pressure, level indicator  260  lights LED  264 . 
     During treatment, airway resistance may be checked to determine the progress of lung clearance. To accomplish this, test switch  220  is pressed so that; it connects terminal  220   a  to terminal  220   c  (see  FIG. 5 ). At this point PFT potentiometer  230  of airway resistance module  200  provides an input to motor drive amplifier  72  (through test switch  220  and summing junction  76 ) and controls air pressure input mouthpiece system  12   b  PFT potentiometer  230  is adjusted until both LED&#39;s  262  and  264  are not lit. This is the null point of pressure within the mouth-the oscillatory air pressure waves induced by chest wall force applicator  12 a are equal and opposite to the oscillatory pressure waves provided at mouthpiece  112  by air pressure input mouthpiece system  12   b . The airflow and air pressure in mouthpiece  112  are at a magnitude equal to that flow caused by the oscillation pressure of chest wall force applicator  12   a  on the patient&#39;s chest, which is transferred to the. patient&#39;s lungs and is then suppressed by the resistance of the mucus in the airways as the air flows through them on the way to the patient&#39;s mouth. The indicator knob position of PFT potentiometer  230  provides a numerical reading of the airway resistance of the patient&#39;s lungs. Using this test, progress can be checked during treatment and from one treatment to the next. All factors except airway resistance should be constant. In an alternative embodiment, a computer algorithm is used to find the null point of pressure and convert that to a numerical value for display or print out. 
     A common method for determining airway resistance measures air flow through a restriction over time. The problems with this method, which are solved with the present invention, are that mucus can clog the restriction, the equipment needs to be calibrated, and it is maneuver-dependent on the patient. These factors can lead to erroneous results. 
       FIGS. 8   a ,  8   b , and  8   c  graph pressure waves from chest wall force  15  applicator  12   a  (vest pressure  300 ) and the patient&#39;s mouth through mouthpiece  112  (mouth pressure  310 ) versus time.  FIG. 8   a  is an illustration of the force from chest wall applicator at a greater pressure than the pressure at the patient&#39;s mouth created by air pressure input mouthpiece system  12   b . This is the situation where LED  262  of airway resistance module  210  would light. The upper waveform  300  is the oscillatory pressure of chest wall force applicator  12   a . The lower waveform  310  is the oscillatory pressure at the patient&#39;s mouth which is the sum of the oscillations from the lungs plus oscillations from the air chamber  84  traveling down tube  110 . 
       FIG. 8   b  is an illustration of waveforms during the null point of pressure. Neither LED ( 262 ,  264 ) would light during this period. Again, the upper waveform  300  is the oscillatory pressure from chest wall force applicator  12   a , and the lower waveform  310  is the pressure at the patient&#39;s mouth through mouthpiece  112 . As described above, the null point of pressure is reached when the outward flow from the patient&#39;s mouth caused by air pressure input mouthpiece system  12   b  almost exactly equals the expiratory flow caused by the compressive force of chest wall force applicator  12   a  on the patient&#39;s chest. Therefore, PFT potentiometer  230 , while defining the flow rate from the. patient&#39;s mouth, is an analog of the airway resistance at the null point of pressure. The small pressure variations seen in the lower waveform  310  are due to imperfections in the phase angle and shape of the two pressure waves producing less than perfect cancellation. Thus, null is indicated by a minimum in the amplitude of this waveform  310 . 
       FIG. 8   c  is an illustration of waveforms  300  and  310  when the pressure in mouthpiece  112 measured from tube 110 is greater than the oscillatory pressure produced by chest wall force applicator  12   a . LED  264  lights in this situation. The wave shape of waveform  310  is the result of the combining of two pressure waves having unequal magnitude and phase. The oscillations on the patient&#39;s chest become out of phase by 180° compared to airflow oscillations at the patient&#39;s mouth. These  FIGS. 8   a – 8   c  show that there is a null point of pressure where the two pressures cancel each other, and on either side of this point non-zero waveforms are generated. 
     One advantage of this system is that the null point of pressure is chosen, so no calibration sequence is required of system components. Another advantage is that it does not require any breathing maneuvers on the part of the patient. Repeatable adherence to a maneuver is necessary for standard pulmonary function testing, therefore, tests relying on breathing maneuvers may be inaccurate, or the data may not be usable. 
     FOURTH EMBODIMENT (FIG.  9 ) 
       FIG. 9  shows a fourth embodiment of apparatus  10  which includes all of the features of the first, second and third embodiments. In this fourth embodiment, each of the systems work together to efficiently remove mucus from the patient&#39;s lungs and provide a means of determining the progress of the treatment. At the same time, patient comfort is maintained during treatment. 
     CONCLUSION 
     Airway treatment apparatus  10  performs in such a way that the patient receiving treatment perceives no external pressure on the chest which may cause discomfort depending on the disease state of the patient. Increased oscillatory airflow velocities can be achieved over prior art vest systems, which is the key to successful lung clearance. By incorporating a mechanism to simulate a cough, outcome measuring airway treatment apparatus  10  provides better lung clearance over other vest systems and induces individuals that are not able to voluntarily cough to simulate coughs. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. For example, although the control systems shown in the figures use analog circuitry, other embodiments use digital logic and programmable devices (such as programmable logic arrays, microcontrollers, or microprocessors) to provide the control functions.