There are two basic patterns of breathing disturbances. The most common and most severe form is called Obstructive Sleep Apnea. Here, muscles of the soft palate at the base of the tongue and the uvula (the small conical, fleshy, tissue hanging from the center of the soft palate) relax and sag, obstructing the airway and making breathing labored and noisy. Collapse of the airway will block breathing entirely. When breathing periodically stops, a listener hears the snoring broken by pauses. As pressure to breathe builds, muscles of the diaphragm and chest work harder. Sleep is then temporarily interrupted (sometimes only for seconds). This in turn activates throat muscles and “uncorks” the airway. The effort is akin to slurping a drink through a floppy, wet straw. A listener hears deep gasps as breathing starts. With each gasp, the sleeper awakens, but so briefly and incompletely that he usually does not remember doing so in the morning. Someone with obstructive sleep apnea may stop breathing for 10 seconds or longer, many times per hour and, even hundreds of times each night.
Each time breathing stops, oxygen in the bloodstream falls and the heart must work harder to circulate blood. Blood pressure rises and, over time, may stay elevated after breathing restarts. The heart sometimes beats irregularly and may even pause for several seconds. This may account for some deaths during sleep of people who went to bed in apparent good health.
Alcohol, sleeping pills and tranquilizers taken at bedtime all further reduce muscle tone and, thus, predispose the airway to collapse.
While most people with obstructive sleep apnea have no obvious physical abnormality that interferes with their breathing during sleep, some conditions may play a contributing role. Some people have a smaller jaw or a smaller opening in the airway at the back of the throat. Some have a large tongue, enlarged tonsils or other tissue that partially block the entrance to the airway. Several of these conditions may exist in the same person.
Obstructive sleep apnea primarily strikes overweight men. A different throat anatomy and female hormones may protect women until menopause. In later years, the gap between the sexes narrows, although it never disappears entirely.
The second type of breathing disturbance is called Central Sleep Apnea. In this form of sleep apnea, the airway may stay open but the diaphragm and chest muscles stop working. Falling levels of oxygen sounds an alarm in the brain, causing the sleeper to awaken and start breathing.
Central sleep apnea becomes more common as people grow older. Perhaps one in four people aged 60 or older experiences some disturbed breathing during sleep. For most problems are mild. The problem becomes more frequent and more severe in those who are ill with various medical and neurological disorders. People with central sleep apnea may be more aware of frequent awakenings than those with obstructive sleep apnea.