Abstract:
There is disclosed a system and method for treating obstructive sleep apnea by terminating an obstructive sleep apnea event before the cessation of breathing occurs. The system comprises one or more microphones capable of detecting breathing sounds within an airway of a person. The microphones generate signals representative of the breathing sounds and send the signals to a controller. The controller uses digital signal processing to identify at least one signal pattern that is associated with a breathing pattern of the person that occurs at the onset of an obstructive sleep apnea event. When the controller detects such a signal pattern, the controller sends an alarm signal to a stimulus generator that creates a stimulus to cause the sleeping person to move in a manner to terminate the obstructive sleep apnea event before cessation of breathing occurs. The obstructive sleep apnea event is terminated without waking the sleeping person.

Description:
This application is a continuation of prior U.S. application Ser. No. 09/641,982 filed on Aug. 17, 2000, now U.S. Pat. No. 6,666,830. 
     CROSS REFERENCE TO RELATED APPLICATION 
     The inventors of the present invention have filed a related patent application entitled “System and Method for Treating Obstructive Sleep Apnea” filed on Aug. 17, 2000 as U.S. application Ser. No. 09/641,983, now U.S. Pat. No. 6,935,335. The related patent application and patent and the inventions disclosed therein are assigned to the assignee of the present invention and are incorporated herein by reference for all purposes as if fully set forth herein. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     The present invention is directed to a system and method for detecting the onset of an obstructive sleep apnea event before cessation of breathing occurs. 
     BACKGROUND OF THE INVENTION 
     Apnea is the cessation of breathing. Sleep apnea is the cessation of breathing during sleep. Sleep apnea is a common sleep disorder that affects over twelve million (12,000,000) people in the United States. Persons with sleep apnea may stop and start breathing several times an hour while sleeping. Each individual episode of the cessation of breathing is referred to as a sleep apnea event. 
     When a person stops breathing during sleep the person&#39;s brain soon senses that oxygen levels in the blood are low and carbon dioxide levels in the blood are high. The brain then sends emergency signals to the body to cause the body to try to increase gas exchange in the lungs to increase the amount of oxygen and to decrease the amount of carbon dioxide. The body&#39;s autonomic physiological reflexes initiate survival reactions such as gasping for air, the production of enzymes to constrict arteries to increase blood pressure, and the production of enzymes to increase heart rate. The person will then usually gasp for air and thereby restore the effective gas exchange of oxygen and carbon dioxide in the lungs. This causes the sleep apnea event to end. 
     The brain may also cause the body&#39;s autonomic physiological reflexes to release large amounts of adrenaline in order to stir the person to gasp for air. Over a period of time repeated rushes of adrenaline in the body can have negative effects and can lead to heart damage and other medical problems. 
     Often the person wakes up while gasping for air. Even if the person does not become conscious while gasping for air, the body&#39;s sleep state is interrupted and the body is physiologically stressed during each sleep apnea event. Sleep apnea events can occur multiple times during a period of sleep. That is, the process of ceasing to breathe, become physiologically stressed, and gasping for air may be repeated numerous times during a period of sleep. Successive sleep apnea events cause a person to experience many short interrupted periods of sleep. 
     Interrupted periods of sleep can produce varying levels of fatigue, lack of energy, and daytime sleepiness. Other symptoms may include restless sleep, loud and sometimes heavy snoring, morning headaches, irritability, mood changes, behavior changes, and similar emotional or physical disorders. While mild forms of sleep apnea may exist without apparent harm to the individual, severe cases may lead to such conditions as weight gain, impotency, high blood pressure, stroke, mental problems, memory loss, and even death. 
     Sometimes sleep apnea directly causes death during sleep due to asphyxiation because of a lack of oxygen. More frequently sleep apnea indirectly causes death because of motor vehicle crashes, job-site accidents, and similar events which are due to sleepiness caused by sleep deprivation. 
     There are two forms of sleep apnea. The two forms are central sleep apnea and obstructive sleep apnea. At the present time, central sleep apnea and obstructive sleep apnea are thought to originate from two different sources. Central sleep apnea appears to be linked to a malfunction of the brain that interferes with neurological signals that normally control the breathing process. Obstructive sleep apnea is caused by a blockage of the breathing airway that completely stops the flow of air to and from the lungs. A common form of obstructive sleep apnea occurs when fleshy tissue in a sleeping person&#39;s throat collapses and seals off the pharyngeal airway. A condition called mixed sleep apnea results when central sleep apnea events and obstructive sleep apnea events alternate. 
     Sometimes central sleep apnea directly causes death during sleep when the sleeping person completely ceases breathing. Death results from asphyxiation due toga lack of oxygen. More frequently obstructive sleep apnea indirectly causes death because of motor vehicle crashes, job-site accidents, and similar events that are due to sleepiness caused by sleep deprivation. 
     Because of the variety and degree of symptoms, diagnosis of obstructive sleep apnea typically requires more than a simple analysis of symptoms. Depending upon the symptoms and severity, diagnosis may include a thorough physical exam, an examination of the mouth and throat for abnormalities, and sleep studies. Thorough sleep studies include additional tests such as electrocardiogram (ECG) tests for detecting arrhythmias, and tests for arterial blood gases to find sleep periods in which the blood oxygen level is below its normal low level. 
     Successful treatment for obstructive sleep apnea must ensure that a person&#39;s breathing passages remain open during sleep. The simplest treatments include weight reduction, change in body position while sleeping, avoidance of alcohol, avoidance of sedatives, and similar changes in lifestyle. When anatomical obstructions are found to be the source of obstructive sleep apnea, surgery may be required for removal of enlarged tonsils, enlarged adenoids, excess tissue at the back of the throat, and similar types of obstructions. In more extreme cases, an opening may be created in the trachea in order to bypass the obstruction that is blocking the airway during sleep. 
     One device for the treatment of obstructive sleep apnea is a device that pumps fresh air into a mask worn over the nose. This device provides what is known as nasal continuous positive airway pressure (CPAP). When the mask and air flow are properly adjusted, the air pressure opens the upper air passage enough to prevent snoring and known forms of apnea. The disadvantages of the CPAP treatment include 1) discomfort and sleep disruption caused by the nose mask and the mechanism for connecting the mask to the air pumping device, and 2) original and on-going cost for the apparatus, and 3) inconvenience when the sleeping location changes. Some newer types of CPAP devices do not use a mask (e.g., the CPAP device disclosed in U.S. Pat. No. 6,012,455). 
     In addition to the more traditional treatments for obstructive sleep apnea described above, alternatives are constantly being studied and developed. Medications are being researched, but no medication has yet been developed which has proven to be effective. Mechanical devices that are inserted into the mouth while sleeping have been tried with varying success. For instance, devices which keep the jaw or tongue in proper position are sometimes effective in cases where breathing is obstructed by a large tongue or a “set back” jaw. However, these devices have some disadvantages. They are uncomfortable to wear during sleep (which causes them to not be regularly used). Each device must have a different design for each specific type of air passage obstruction. Each device must be individually sized for each patient. 
     More recently, systems have been developed for the purpose of clearing upper airway passages during sleep using the electrical stimulation of nerves or muscles. In some cases, these systems require surgical implantation of sensors and associated electronics that detect when breathing has ceased and then stimulate the breathing process. Some hybrid systems have been developed that require surgical insertion of one or more sensors plus external equipment for monitoring the breathing process or moving the obstruction when breathing ceases. These systems may produce positive results but they also have associated risks due to surgery, may need replacement at later times (requiring additional surgery), and may have higher costs and lower reliability than the more traditional treatments. In addition, the hybrid systems also have the accompanying physical restrictions and accompanying disadvantages associated with connections to the external equipment. 
     Therefore, there is a need in the art for an improved system and method for treating obstructive sleep apnea. In particular, there is a need in the art for a system and method that does not create other types of sleep disturbing effects, does not require surgical implementation, and does not have the high costs associated with some of the types of treatments currently in use. 
     Prior art systems and methods are directed toward detecting and treating an obstructive sleep apnea event after the obstructive sleep apnea event has occurred. It would be very advantageous, however, to be able to detect the onset of an obstructive sleep apnea event before the obstructive sleep apnea event fully develops. That is, if the onset of an obstructive sleep apnea event can be detected before the sleeping patient actually stops breathing, steps can be taken to prevent the obstructive sleep apnea event from occurring. 
     Therefore, there is a need for a system and method for detecting the onset of an obstructive sleep apnea event before the obstructive sleep apnea event fully develops. In particular, there is a need for a system and method for detecting the onset of an obstructive sleep apnea event before the cessation of breathing occurs. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a system and method for detecting the onset of an obstructive sleep apnea event before the sleep apnea event fully develops into cessation of breathing. 
     The system of the present invention comprises one or more microphones that are capable of detecting breathing sounds within an airway of a sleeping person. The microphones generate signals that are representative of the detected breathing sounds and transfer the signals to a controller. The controller identifies at least one signal pattern that is associated with a breathing pattern of the person that occurs at the onset of an obstructive sleep apnea event. The controller may also identify at least one signal pattern that is associated with a partially occluded breathing pattern of the person. The controller identifies the signal patterns by using digital signal processing techniques to analyze the signals that are representative of breathing sounds. 
     It is a primary object of the present invention to provide a system and method for detecting the onset of an obstructive sleep apnea event before the obstructive sleep apnea event fully develops into cessation of breathing. 
     It is also an object of the present invention to provide a controller that is capable of receiving signals that are representative of breathing sounds of a person and identifying within the signals at least one signal pattern that is associated with a breathing pattern of the person that occurs at the onset of an obstructive sleep apnea event. 
     It is also an object of the present invention to provide a controller that is capable of receiving signals that are representative of breathing sounds of a person and identifying within the signals at least one signal pattern that is associated with a partially occluded breathing pattern of the person. 
     It is a further object of the present invention to provide a controller that is capable of sending an alarm signal to a base station when the controller identifies a signal pattern that may indicate the onset of an obstructive sleep apnea event. 
     It is an object of the present invention to provide a controller that is capable of receiving an airflow detection signal from an airflow sensor to determine the breathing rate of a person who is subject to the onset of an obstructive sleep apnea event. 
     It is also an object of the present invention to provide a controller that is capable of identifying signal patterns by using digital signal processing techniques to analyze signals that are representative of breathing sounds. 
     It is a further object of the present invention to provide a method for detecting breathing sounds within an airway of a sleeping person, and generating signals that are representative of the breathing sounds, and identifying within the signals at least one signal pattern that is associated with a breathing pattern of the person that occurs before the onset of an obstructive sleep apnea event. 
     The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form. 
     Before undertaking the Detailed Description, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise” and derivatives thereof mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware, or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document. Those of ordinary skill in the art should understand that in many, if not most, instances, such definitions apply to prior, as well as future uses of such defined words and phrases. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, wherein like numbers designate like objects, and in which: 
         FIG. 1  is diagram illustrating a plurality of microphones and a controller mounted on a collar around the neck of a person whose breathing is being monitored; 
         FIG. 2  is a circuit diagram illustrating the connection of the plurality of microphones in  FIG. 1  to the controller of the present invention; 
         FIG. 3  is a circuit diagram illustrating the connection of the controller of the present invention with a base station and illustrating a communication link between a chest motion sensor and the base station; and 
         FIG. 4  is a diagram illustrating one microphone and the controller of the present invention mounted on a collar around the neck of a person whose breathing is being monitored; and 
         FIG. 5  is a flow diagram illustrating an advantageous embodiment of the method of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 through 5 , discussed below, and the various embodiments used to describe the principles of the present invention in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the invention. Those skilled in the art will understand that the principles of the present invention may be implemented in any suitably modified system for detecting the onset of an obstructive sleep apnea event. 
       FIG. 1  illustrates one embodiment of the present invention showing how apparatus  100  of the present invention may be attached to a person  120  who suffers from sleep apnea. Apparatus  100  may comprise either one microphone or a plurality of microphones. The embodiment of the present invention that is illustrated in  FIG. 1  has four microphones  125 ,  130 ,  135 , and  140 . It is noted, however, that it is possible to practice the present invention using only one microphone. The embodiment of the present invention that is illustrated in  FIG. 4  has only one microphone  125 . 
     Microphones  125 ,  130 ,  135 , and  140 , are each capable of being acoustically associated with person  120 . Microphones  125 ,  130 ,  135 , and  140 , are each capable of detecting sounds within a breathing airway of person  120 . One type of microphone that is suitable for use in the present invention is the electret microphone. Microphones  125 ,  130 ,  135 , and  140 , are each attached to collar  145  and collar  145  is detachably fastened around the neck of person  120 . Collar  145  may be fastened around the neck of person  120  with a velcro clasp .(not shown in  FIG. 1 ). Collar  145  is fastened around the neck of person  120  so that microphones  125 ,  130 ,  135 , and  140 , are positioned adjacent a breathing airway in the neck of person  120 . 
     Each of the microphones  125 ,  130 ,  135 , and  140 , is capable of generating signals representative of the sounds of breathing of person  120 . When microphones  125 ,  130 ,  135 , and  140 , detect sounds of breathing, then each microphone generates a signal. The signals generated by each microphone are transferred via an individual microphone signal line to signal processing circuitry  200  (shown in  FIG. 2 ) contained within housing  150 . 
     Apparatus  100  may optionally be used in conjunction with an airflow sensor  155  (shown schematically in  FIG. 2 ). Airflow sensor  155  is preferably attached near the nostrils of person  120 . Airflow sensor  155  is capable of detecting a flow of air in and out of the nostrils of person  120  and is capable of determining the breathing rate of person  120 . Airflow sensor  155  may also be located within other locations in an airway of person  120 . Airflow sensors are typically capable of detecting flows of air between frequencies of one tenth Hertz (0.1 Hz) and one and one tenth Hertz (1.1 Hz). 
     When airflow sensor  155  detects a flow of air, then airflow sensor  155  generates an airflow detection signal. The airflow detection signal generated by airflow sensor  155  is transferred via a signal line to signal processing circuitry  200  (shown in  FIG. 2 ) contained within housing  150 . Signal processing circuitry  200  monitors the airflow detection signal of airflow sensor  155  to determine the breathing rate of person  120 . 
     Housing  150  is mounted on collar  145  as shown in  FIG. 1 . Signal processing circuitry  200  within housing  150  may be connected via signal lines (not shown in  FIG. 1 ) to base station  310  (shown in  FIG. 3 ) located remotely from the site where person  120  is sleeping. In an alternative embodiment, signal processing circuitry  200  may transmit signal information to base station  310  through radio frequency receiver  320  (shown in  FIG. 3 ) using a radio frequency transmitter (not shown) located within housing  150 . In another alternative embodiment, signal processing circuitry  200  may transmit signal information to a network site (not shown) such as a site connected to the Internet. 
       FIG. 2  is a circuit diagram illustrating the connection of microphones  125 ,  130 ,  135 , and  140 , and optional airflow sensor  155  to controller  230  within signal processing circuitry  200 . Signals from microphone  125  are transferred to amplifier.  210  where the signals are amplified. Similarly, signals from microphone  130  are amplified in amplifier  215 , signals from microphone  135  are amplified in amplifier  220 , and signals from microphone  140  are amplified in amplifier  225 . The amplified signals from amplifiers  210 ,  215 ,  220 , and  225  are then transferred to controller  230 . 
     Signals from airflow sensor  155  are transferred to amplifier  235  where the signals are amplified. The amplified signals from amplifier  235  are then transferred to controller  230 . 
     Signals from amplifier  210  are also transferred to filter  240  (Filter  1 ) where the signals are filtered. In one advantageous embodiment filter  240  filters out all signals except signals having frequencies in the range of twenty Hertz (20 Hz) to one hundred Hertz (100 Hz). The filtered signals from filter  240  are then transferred to controller  230 . 
     Similarly, signals from amplifier  215  are also transferred to filter  245  (Filter  2 ) where the signals are filtered. In one advantageous embodiment filter  245  filters out all signals except signals having frequencies in the range of one hundred Hertz (100 Hz) to one thousand Hertz (1,000 Hz). The filtered signals from filter  245  are then transferred to controller  230 . 
     Similarly, signals from amplifier  220  are also transferred to filter  250  (Filter  3 ) where the signals are filtered. In one advantageous embodiment filter  250  filters out all signals except signals having frequencies in the range of one thousand Hertz (1,000 Hz) to ten thousand Hertz (10,000 Hz). The filtered signals from filter  250  are then transferred to controller  230 . 
     Lastly, signals from amplifier  225  are also transferred to filter  255  (Filter  4 ) where the signals are filtered. In one advantageous embodiment filter  250  filters out all signals except signals having frequencies in the range of ten thousand Hertz (10,000 Hz) to twenty thousand Hertz (20,000 Hz). The filtered signals from filter  255  are then transferred to controller  230 . 
     The numerical values given for the frequency ranges are illustrative only. It is clear that other ranges of frequency values may be used to practice the invention. 
     Controller  230  receives a complete set of filtered and unfiltered signals from microphones  125 ,  130 ,  135 , and  140 . Controller  230  also receives an airflow detection signal from airflow sensor  155 . The signals from microphones  125 ,  130 ,  135 , and  140  will be collectively referred to as the “microphone signals.” As will be more fully explained, controller  230  uses information from the microphone signals to identify a signal pattern that is associated with a breathing pattern of person  120  that occurs at the onset of an obstructive sleep apnea event. 
     As shown in  FIG. 3 , controller  230  is coupled to base station  310 . Controller  230  continually transfers signals to base station  310  concerning the status of the breathing of person  120 . An operator of base station  310  can monitor any of the signals within controller  230 . Whenever controller  230  identifies a signal pattern that is associated with a breathing pattern of person  120  that occurs at the onset of an obstructive sleep apnea event, controller  230  initiates an obstructive sleep apnea event onset alarm and sends the obstructive sleep apnea event onset alarm to base station  310 . Similarly, whenever controller  230  receives no signals from microphones  125 ,  130 ,  135 , and  140 , then controller  230  assumes that person  120  is not breathing. Controller  230  then immediately initiates a “no breathing” alarm and sends the “no breathing” alarm to base station  310 . 
     Base station  310  is also coupled to radio frequency receiver  320  having receiver antenna  330  for receiving radio frequency transmissions from radio frequency transmitter  340  through transmitter antenna  350 . Radio frequency transmitter  340  is coupled to a chest motion sensor  360  that is coupled to the chest of person  120 . Chest motion sensor  360  senses the rhythmical motion of the chest of person  120  during breathing. In this manner, radio frequency transmitter  340  continually transfers signals to base station  310  concerning the status of the chest motion of person  120 . 
     Controller  230  comprises software for analyzing the microphone signals. The software in controller  230  utilizes digital signal processing techniques for finding the frequency domain components of each microphone signal. The digital signal processing techniques used by controller  230  may be of any type including, without limitation, Fast Fourier Transform techniques. Controller  230  also comprises memory unit  260  that is capable of storing 1) digital signal processing analysis software for analyzing the microphone signals, and 2) signal patterns that result from the digital signal processing analysis of the microphone signals, and 3) software for comparing signal patterns. 
     Controller  230  is capable of identifying and storing signal patterns from the microphone signals. For example, when person  120  is breathing normally, controller  23   b  receives microphone signals that indicate normal breathing. The signal pattern that results from the digital signal processing analysis of the “normal breathing” microphone signals is stored in memory unit  260  as a “normal breathing” signal pattern. Controller  230  is capable of recalling the “normal breathing” signal pattern from memory unit  260  in order to compare other signal patterns with the “normal breathing” signal pattern. 
     A person who suffers from sleep apnea will often exhibit a breathing pattern in which the flow of air through an airway is partially occluded. This means that at least one portion of the airway is not fully open. Although air flows through the airway, the air is constricted as it passes through the partially occluded airway. The sound of air as it passes through a partially occluded airway differs from the sound of air as it passes through a fully open airway. That is, the sound of partially occluded breathing has different sound characteristics than the sound of normal breathing. 
     When person  120  begins to exhibit a breathing pattern in which the flow of air is partially occluded, then controller  230  receives microphone signals that are indicative of partially occluded breathing. The signal pattern that results from the digital signal processing analysis of the “partially occluded breathing” microphone signals is stored in memory unit  260  as a “partially occluded breathing” signal pattern. Controller  230  is capable of recalling the “partially occluded breathing” signal pattern from memory unit  260  in order to compare other signal patterns with the “partially occluded breathing” signal pattern. 
     While person  120  is breathing, controller  230  is capable of monitoring the microphone signals that are representative of the breathing sounds. Controller  230  is also capable of obtaining the signal patterns that result from the digital signal processing analysis of the microphone signals. Controller  230  is also capable of comparing the current signal patterns with the “partially occluded breathing” signal pattern. When controller  230  determines that a current signal pattern is substantially the same as the “partially occluded breathing” signal pattern, then controller  230  sends an alarm signal to base station  310 . The alarm signal indicates that at least one signal pattern has been identified that is associated with a partially occluded breathing pattern. 
     At the onset of an obstructive sleep apnea event, a person may exhibit a breathing pattern in which the flow of air through an airway differs from normal breathing. In such cases, the sound of air as it passes through the airway at the onset of an obstructive sleep apnea event differs from the sound of air as it passes through a fully open airway. That is, the sound of breathing at the onset of an obstructive sleep apnea event has different sound characteristics than the sound of normal breathing. 
     When person  120  begins to exhibit a breathing pattern associated with the onset of an obstructive sleep apnea event, then controller  230  receives microphone signals that are indicative of “apnea onset breathing.” The signal pattern that results from the digital signal processing analysis of the “apnea onset breathing” microphone signals is stored in memory unit  260  as an “apnea onset breathing” signal pattern. Controller  230  is capable of recalling the “apnea onset breathing” signal pattern from memory unit  260  in order to compare other signal patterns with the “apnea onset breathing” signal pattern. 
     While person  120  is breathing, controller  230  is capable of monitoring the microphone signals that are representative of the breathing sounds. Controller  230  is also capable of obtaining the signal patterns that result from the digital signal processing analysis of the microphone signals. Controller  230  is also capable of comparing the current signal patterns with the “apnea onset breathing” signal pattern. When controller  230  determines that a current signal pattern is substantially the same as the “apnea onset breathing” signal pattern, then controller  230  sends an alarm signal to base station  310 . The alarm signal indicates that at least one signal pattern has been identified that is associated with a breathing pattern that occurs at the onset of an obstructive sleep apnea event. 
     After controller  230  signals that person  120  is exhibiting a breathing pattern that is associated with the onset of an obstructive sleep apnea event, steps may be taken to stimulate the body of person  120  in a manner that will terminate the obstructive sleep apnea event before cessation of breathing occurs. 
     As previously described, controller  230  may receive an airflow detection signal from airflow sensor  155 . Controller  230  is capable of determining from the airflow detection signal when person  120  is inhaling and exhaling. Controller  230  is also capable of determining from the microphone signals when person  120  is inhaling and exhaling. In an alternate advantageous embodiment of the present invention, controller  230  shuts down and ceases monitoring the signal patterns 1) during exhalation, or 2) during inhalation. By operating only during one half of the respiratory cycle, controller  230  uses only one half of the power that would otherwise be required. 
     If the onset of obstructive sleep apnea fully develops, then cessation of breathing will occur. When person  120  ceases to breathe, then microphones  125 ,  130 ,  135 , and  140 , detect no breathing sounds. When controller  230  receives signals that indicate that a “no breathing” condition has occurred, then controller  230  sends a “no breathing” alarm as previously described. 
       FIG. 5  illustrates a flow chart  500  depicting the operation of one advantageous embodiment of the present invention. First, microphones  125 ,  130 ,  135 , and  140 , detect sounds of breathing in an airway of person  120  (process step  505 ) and generate signals that are representative of the breathing sounds (process step  510 ). Controller  230  then analyzes the signals using digital signal processing software (e.g., Fast Fourier Transform analysis software) to generate signal patterns that are representative of the signals (process step  515 ). 
     Controller  230  monitors the signal patterns to identify a signal pattern that is associated with a breathing pattern that occurs at the onset of an obstructive sleep apnea event (process step  520 ). Controller  230  then sends an alarm to base station  310  that indicates that controller  230  has detected a signal pattern that is associated with a breathing pattern that occurs at the onset of an obstructive sleep apnea event (process step  525 ). 
     Although the present invention has been described in detail, those skilled in the art should understand that they can make various changes, substitutions and alterations without departing from the spirit and scope of the invention in its broadest form.