Abstract:
Substantially constant positive airway pressure systems and methods mediate the variations in pressures that occur within a conventional CPAP mask during inhalation and exhalation cycles, and thereby reduce discomfort.

Description:
RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/402,496, filed Aug. 31, 2010, and entitled “Substantially Constant Positive Airway Pressure Systems and Methods for Treating Sleep Apnea, Snoring, and Other Respiratory Disorders,” which is incorporated herein by reference. This application is also a continuation-in-part of co-pending U.S. patent application Ser. No. 12/655,829, filed Jan. 8, 2010, entitled “Self-Contained, Intermittent Positive Airway Pressure Systems and Methods for Treating Sleep Apnea, Snoring, and Other Respiratory Disorders,” which claims the benefit of U.S. Provisional Patent Application Ser. No. 61/143,371, filed Jan. 8, 2009, and entitled “Devices and Methods for Treating Respiratory Disorders,” which are also incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention generally relates to respiration aids to prevent partial or complete airway blockage during sleep, or other respiratory disorders. The invention also generally relates to positive airway pressure systems and methods. 
       BACKGROUND OF THE INVENTION 
       [0003]    During sleep, all muscles, including those of the upper airway, lose tone and relax. Obstructive Sleep Apnea (OSA) occurs when tissue blocks the upper airway during sleep. This will cause a drop in blood oxygen and a rise in blood carbon dioxide. The brain will sense these changes, and awaken the person enough to restore muscle tone to the structures of the upper airway, and the airway will reopen. 
         [0004]    The severity of OSA is determined by the number of blockages per hour of sleep, also called the apnea-hypopnea index (AHI). These include complete blockages (apneas) and partial blockages (hypopneas). The severity of OSA, as determined by a sleep study, is classified as follows: 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Severity 
                 Blockages per Hour (AHI) 
               
               
                   
                   
               
             
             
               
                   
                 Mild 
                  5-15 
               
               
                   
                 Moderate 
                 15-30 
               
               
                   
                 Severe 
                 30+ 
               
               
                   
                   
               
             
          
         
       
     
         [0005]    OSA disrupts restorative sleep. Chronic fatigue has long been recognized as the hallmark of OSA. But more recently, large clinical studies have shown a strong link between OSA and stroke and death. This link is independent of other risk factors for cardiovascular disease such as hypertension, obesity, high cholesterol, smoking and diabetes. 
       Current Therapies 
       [0006]    Several structures can cause blockage of the upper airway: the tongue, the soft palate, the lateral walls of the pharynx, the tonsils and the epiglottis. In most patients, the blockage is caused by a combination of these anatomical structures. 
         [0007]    Many procedures and devices have been used to stabilize, modify or remove tissue in the airway to treat OSA. In uvulopalatopharygoplasty (UPPP), the uvula, part of the soft palate and the tonsils are removed. The Repose stitch is used to tie the tongue to the mandible to prevent its posterior movement. Oral appliances move the mandible forward (very slightly) to create more space in the airway. 
         [0008]    None of these approaches has achieved much more than a 50% success rate, with success defined as a 50% decrease in AHI to a score below 20. The limited success of these approaches likely stems from the fact that they don&#39;t address all anatomical sources of a blockage. 
         [0009]    The most widely used therapy for OSA is Continuous Positive Airway Pressure, or CPAP. With CPAP, a bedside console provides a continuous flow of air through a connecting tube to a mask that forms an airtight seal around the nose or nose and mouth. There is an exit hole for the air (both from the compressor and that exhaled by the patient), usually near the junction of the tubing to the compressor and the mask. The compressor within the console spins at a constant level, set by a medical professional, to achieve a sufficient pressure to maintain airway patency during sleep. The pressure provided by CPAP (at a level set by a medical professional) needs to be sufficient to prevent airway collapse during the most vulnerable point in the respiratory cycle, the peak of inhalation. 
         [0010]    But even though the compressor spins at a constant speed, the pressure achieved in the mask and in the airway will vary through the respiratory cycle. As a patient with CPAP inhales, pressure in the mask (and the upper airway) will drop. When a patient exhales, pressure will increase. This is because a CPAP patient is drawing from and giving to a limited reservoir of air within the mask and tube. The exit hole and compressor in this system cannot maintain a constant pressure in the mask as a person breathes. Because inhalation lowers pressure in the mask, this will mean the pressure provided by the compressor will be higher than necessary to prevent airway collapse during the rest of the respiratory cycle. 
         [0011]    Contrast the CPAP situation to the situation of a person who is not using CPAP. This person draws air from a room and exhales into a room. Because the reservoir of air is so large (i.e., the volume of the room) relative to the volume of the lungs, the subtraction of air from the room (during inhalation) and the addition of air to the room (during expiration) have little effect on the air pressure within the room (and it is largely offset by the expansion and contraction of the torso). Thus a person breathing normally experiences very little variation in air pressure in the proximal portions of the airway (the nose and the mouth). 
         [0012]    However, for the reasons explained, a patient with CPAP will not only experience air pressures higher than atmospheric pressure (because of the compressor), the patient will also experience more pressure variation throughout the respiratory cycle than someone who is not using CPAP. 
         [0013]    Baroreceptors in the nasal passages are very sensitive to pressure changes. The more the pressure in the nasal passages varies through the respiratory cycle, the less comfortable the patient will be, and the more likely to wake up during sleep, thus defeating the purpose of CPAP. 
         [0014]    Roughly half of all patients who try CPAP are unable to sleep with it. One aspect of CPAP that patients dislike arises from the discomfort caused by experiencing variable pressures within the CPAP mask. These make CPAP less comfortable, and contribute to the poor compliance with CPAP. 
       Summary of the Technical Features of the Invention 
       [0015]    The invention provides substantially constant positive airway pressure systems and methods that mediate the variations in pressures that occur within a conventional CPAP mask during inhalation and exhalation cycles, and thereby reduce discomfort. 
         [0016]    In one embodiment, the system and methods include one or more pressure and/or flow sensors communicating with the interior of the CPAP mask. A master controller is coupled to the pressure and/or flow sensors. The master controller operates the CPAP air compressor according to pre-programmed rules (executing prescribed control algorithms) in response to pressure and/or flow conditions sensed by the pressure and/or flow sensors. According to the pre-programmed rules, the master controller operates the air compressor to achieve essentially constant pressure conditions within the mask during inhalation and exhalation, or pressure conditions within the mask that do not exceed or fall below a specified minimal range of pressures. 
         [0017]    In another embodiment, the systems and methods include one or more one-way relief valves on the CPAP mask, or tubing connecting the compressor and the mask or on the compressor. The relief valve or valves are closed when pressure in the mask is below a specified magnitude. When pressure in the mask is at or above the specified magnitude, the relief valve or valves open in a one way flow direction to vent air out of the mask, thereby relieving the pressure until it drops below the specified magnitude, at which time the relief valve or valves close. The relief valve or valves accommodate airflow sufficient to allow quick pressure relief within the mask. Alternatively, the relief valves can comprise electrically actuated valves controlled by the master controller. 
         [0018]    The technical features of the substantially constant positive airway pressure systems and methods would allow a CPAP device to maintain a narrower pressure range within the mask than current CPAP devices can. This would be more comfortable for the wearer, and should improve compliance. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a diagrammatic view of a conventional CPAP system. 
           [0020]      FIG. 2  is a graph showing the variation of pressure within a mask when coupled to the conventional CPAP system shown in  FIG. 1  during an individual&#39;s inhalation and exhalation cycles. 
           [0021]      FIG. 3  is a diagrammatic view of one embodiment of a substantially constant positive airway pressure system that embodies technical features of the invention. 
           [0022]      FIG. 4  is a graph showing the substantially constant pressure maintained within a mask when coupled to the substantially constant positive airway pressure system shown in  FIG. 3  during an individual&#39;s inhalation and exhalation cycles. 
           [0023]      FIG. 5  is a diagrammatic view of another embodiment of a substantially constant positive airway pressure system that embodies technical features of the invention. 
           [0024]      FIGS. 6A and 6B  show the operation of a one way pressure relief valve that the substantially constant positive airway pressure system shown in  FIG. 5  incorporates. 
           [0025]      FIG. 7  is a graph showing the substantially constant pressure maintained within a mask when coupled to the substantially constant positive airway pressure system shown in  FIG. 5  during an individual&#39;s inhalation and exhalation cycles. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0026]    Although the disclosure hereof is detailed and exact to enable those skilled in the art to practice the invention, the physical embodiments herein disclosed merely exemplify the invention, which may be embodied in other specific structures. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims. 
       I. The Problem: An Overview 
       [0027]      FIG. 1  shows a conventional CPAP system  10 . A conventional CPAP system  10  consists of three main components: an airtight mask  12  fitting in or over the nose or nose and mouth; an air pressurizing console  14  that includes an air compressor  16 ; and a tube  18  connecting the two. There is an exit hole  20  for the air (both from the compressor  16  and that exhaled by the patient), usually near the junction of the tube  18  to the compressor  16  and the mask  12 . 
         [0028]    The air compressor  16  spins at a constant speed to provide a flow of air at a constant pressure to the mask  12 . The magnitude of the speed (and thus the pressure) is set by a medical professional to prevent airway collapse during the most vulnerable point in the respiratory cycle, which is at the peak of inhalation. 
         [0029]    Because the air compressor  16  spins at a constant speed to provide a flow of air at a constant pressure to the mask  12 , the pressure within the mask  12  and in the airway will vary as a result of the individual&#39;s inhalation and exhalation into the mask  12  during the respiratory cycle. This variation is shown in  FIG. 2 . 
         [0030]    As the patient wearing the mask  12  inhales, pressure in the mask  12  (and the upper airway) will drop, because inhalation removes a volume of air from the mask  12  into the airway. The air compressor  16  is set to assure that, during inhalation, the pressure in the mask  12  and the airway nevertheless remains at a high enough level so that airway does not collapse; in effect, the air compressor inflates the airway. Thus, the pressure sensed in the mask  12  by baroreceptors in the individual&#39;s nasal passages during inhalation will be higher than would be sensed if the mask was not worn (and the airway perhaps collapsed). 
         [0031]    When the patient exhales, pressure in the mask  12  will increase, because exhalation adds the exhaled volume of air to volume of pressurized air already supplied to the mask  12 . Because the air compressor  16  is spinning at the same speed during exhalation as it is during inhalation, the pressure in the mask  12  sensed by baroreceptors in the individual&#39;s nasal passages during exhalation will also be higher than would be sensed if the mask  12  was not worn. That is because the pressure provided by the compressor  16  must compensate for a decrease in mask pressure during inhalation to prevent airway collapse, so the pressure provided by the compressor  16  to the mask  12  during the rest of the respiratory cycle will of course be higher than necessary to prevent airway collapse. 
         [0032]    Thus, during CPAP, not only are the absolute pressures sensed by baroreceptors in the individual&#39;s nasal passages higher, particularly during exhalation, the variation in these pressures that occur between inhalation and exhalation are far more noticeable when the mask  12  is worn, than when breathing without a mask  12  in an ambient atmosphere. During CPAP, both the sensed existence of higher absolute pressures in the mask  12  and the heightened variation of these pressures in the mask  12  during the respiration cycle can lead to discomfort. 
       II. Feedback Controlled Substantially Constant Mask Pressure 
       [0033]      FIG. 3  shows a substantially constant positive airway pressure system  22  for treating sleep apnea, snoring, and other respiratory disorders. The system  22  comprises an airtight mask  24  fitting in or over the nose or nose and mouth; an air pressurizing console  26  that includes an air compressor  28  coupled to a master controller  30  and tubing  32  connecting the two. 
         [0034]    According to the invention, the system includes one or more pressure and/or flow sensors  34  that communicate with the interior of the mask. The one or more pressure and/or flow sensors  34  can be carried within the mask  24  itself, or in the tubing  32  that leads to the mask, or a combination thereof. 
         [0035]    The master controller  30  is coupled to the pressure and/or flow sensors  34 . The master controller  30  operates the air compressor  28  according to pre-programmed rules (executing prescribed control algorithms) in response to pressure and/or flow conditions sensed by the pressure and/or flow sensors  34  communicating with the mask  24 . According to the pre-programmed rules, the master controller  30  operates the air compressor  28  to achieve substantially constant pressure conditions within the mask  24  during inhalation and exhalation, or pressure conditions within the mask  24  that do not exceed or fall below a specified minimal range of pressures. 
         [0036]    A caregiver can input through a user interface a desired pressure or pressure range to be maintained within the mask  24 . The sensors  34  communicating with the mask  24  provide sensed condition signals to the master controller  30 . The master controller  30  operates the air compressor  28  according to pre-programmed rules in response, at least in part, to the sensed condition signals in a controlled and coordinated fashion, to maintain the desired substantially constant pressure or pressure range within the mask  24 . For example, if the air pressure sensed in the mask  24  falls below that range or level, the master controller  30  commands the compressor  28  to speed up to increase the pressure. If the air pressure sensed in the mask  24  rises above that range or level, the master controller  30  commands the compressor  28  to slow down, allowing pressure to drop. 
         [0037]    The preprogrammed rules can provide control commands that are proportional to sensed absolute deviations from control threshold(s). Alternatively, the preprogrammed rules can provide integral or derivative control commands that are based upon the changes in the deviations over time (increasing? or decreasing?) as well as the rate of the changes in the deviations (i.e., by sensing whether the deviations are getting larger or smaller over time and by how much). 
         [0038]      FIG. 4  demonstrates how the master controller  30  maintains the substantially constant pressure or pressure range within the mask  24  in response to pressure and/or flow conditions sensed by the pressure and/or flow sensors  34  communicating with the mask  24 . 
         [0039]    The system  22  that embodies the technical features just described can be incorporated into either a traditional CPAP system, or one in which the entire system (including the compressor and power source) is worn by the patient. A caregiver can input to the master controller  30  a desired pressure or pressure range for the mask  24 , and the master controller  30  maintains the pressure or pressure range in the mask  24  in the manners just described. 
         [0040]    Such a system  22  would also work if the expiration opening(s) in the CPAP mask  24  were small enough to significantly restrict the flow of expired air, thereby using the patient&#39;s own expiratory pressure to increase pressure in the mask  24  and upper airway during the expiratory phase of the breathing cycle. The pressure and/or flow sensor(s)  34  communicating with the mask  24  would maintain pressure in the mask  24  at a constant level or within a specified range, while a combination of the compressor  28  and the force of expiration both contribute to the pressure in the mask  24 . 
         [0041]    The preprogrammed rule of the master controller  30  could also adapt to the wearer&#39;s breathing pattern. For example, if pressure routinely dropped near the end of each exhalation, the master controller  30  could direct the air compressor  28  to speed up in anticipation of this drop, thereby preventing the pressure in the mask  24  from dropping below the specified value or range. 
       III. One-Way Relief Valves to Provide Substantially Constant Mask Pressure 
       [0042]      FIG. 5  shows another embodiment of a constant positive airway pressure system  36  for treating sleep apnea, snoring, and other respiratory disorders. The system  36  comprises an airtight mask  38  fitting in or over the nose or nose and mouth; an air pressurizing console  40  that includes an air compressor  42 ; and tubing  44  connecting the two. 
         [0043]    According to the invention (see FIGS.  6 A/B and  7 ), the system  36  includes one or more one-way relief valves  46  on the CPAP mask  38 , or tubing connecting the compressor  42  and the mask  38 , or on the compressor  42 . The relief valve or valves  46  are normally closed when pressure in the mask  38  is below a specified magnitude (as  FIG. 6A  shows). When pressure in the mask  38  is at or above the specified magnitude, the relief valve or valves  46  open in a one way flow direction to vent air (see  FIG. 6B ), thereby relieving the pressure until it drops below the specified magnitude, at which time the relief valve or valves  46  close. The relief valve or valves  46  accommodate airflow sufficient to allow quick pressure relief within the mask  38 . 
         [0044]    As  FIG. 7  shows, the opening and closing of the relief valve or valves  46  maintain a narrow pressure range within the CPAP mask  38  through the respiratory cycle without having to alter the speed of the compressor  42 . As a result, the variations in pressure within the mask  38  would be minimal (i.e. less disruptive to the individual during sleep) and the pressure at all times could be the minimum needed to maintain airway patency. 
         [0045]    The specified magnitude of pressure at which a given relief valve  46  opens could be set by a caregiver, e.g., using a special tool. Alternatively, a variety of masks could be made, each with a relief valve or valves  46  preset to a specified pressure (e.g., 8 cm H2O, 9 cm H2O, 10 cm H2O, etc.). Having different masks would be less expensive to manufacture than having an adjustable relief valve, and much less expensive than having a pressure or flow sensor in the mask  38  which would determine the compressor speed. 
         [0046]    The compressor  42  could be set at a constant speed to provide the critical pressure needed to maintain airway patency during peak inhalation. At this point the relief valve or valves  46  would be closed or open only minimally. When the patient is exhaling, the increased pressure in the mask  38  would open the relief valve, and pressure within the mask  38  would not increase much. The valve would also be open somewhat when the patient is neither inhaling nor exhaling. 
         [0047]    The relief valve or valves  46  could be either an “all or nothing” valve (either fully open or fully closed), or it could be a variable relief valve that opens more as pressure increases. 
         [0048]    Alternatively, or in combination, the relief valve or valves  46  can comprise a low-power electrically or pneumatically actuated valve, which are coupled to the master controller  30  and which open and close according to preprogrammed rules in the master controller  30 . As governed by the preprogrammed rules, the “smart” relief valves  46  open and close at different times during the respiratory cycle, so that air from the compressor  42  is not vented to the atmosphere unintentionally. 
         [0049]    The system can further include a passive valve that opens to let air into the mask  38  if the pressure in the mask  38  falls below room pressure. This valve would add a measure of safety should the compressor  42  fail or malfunction. 
         [0050]    Such a system could be employed in either a traditional CPAP system, or one in which the entire system (including the compressor  42  and power source) is worn by the patient. This embodiment of the invention would allow a CPAP device to maintain a narrower pressure range within the mask  38  than current CPAP devices can. This would be more comfortable for the wearer, and thus improve compliance. 
         [0051]    The technical features just described would allow a CPAP device to maintain a narrower pressure range within the mask  38  than current CPAP devices can. This would be more comfortable for the wearer, and should improve compliance. The above-described embodiments of this invention are merely descriptive of its principles and are not to be limited. The scope of this invention instead shall be determined from the scope of the following claims, including their equivalents.