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Sleep Apnea: The Noisy Killer
Dr. Ali is a visiting scientist in the Division of Geriatric Medicine at Saint Louis University Health Science Center.
Like snoring, sleep apnea is much older than Shakespeare, but only recently has it been understood as something different from ordinary snoring, and as a potentially deadly disease. Depending on its severity and its cause, sleep apnea is associated with a variety of heart and breathing problems, including heart arrhythmias, high blood pressure, hardening of the arteries, even heart failure and death. It is a peculiarity of this noisy disease that it announces itself to everyone within earshot -- except its victims.
The medical definition of sleep apnea is a temporary stoppage of breathing during sleep, occurring at least 30 times during the night. The stoppage must be longer than the usual interval between breaths while asleep. Ten seconds is normal for adults.
There are three basic kinds of sleep apnea: the pure central type (CSA), which is caused by problems with the lungs or the breathing mechanism itself; the obstructive type (OSA), in which an obstruction interferes with normal airflow; and mixed sleep apnea (MSA), which combines features of both. Because the vast majority of cases are obstructive, when people discuss sleep apnea, most of the time they are referring to OSA.
Sleep apnea is an extremely common condition in older persons, occurring in at least 50% of persons over 60 years.(1) For comparison, sleep apnea occurs in only 6% of middle aged women and 9% of middle aged men.
The History of Sleep ApneaBoth central and obstructive apnea had been observed by doctors as early as 1877. Later, researchers Osler and Burwell(2) named the combination of obesity; hypersomnolence, or excessive sleepiness; and inadequate airflow to the lungs during sleep as "Pickwickian Syndrome," after a loud-snoring character from Charles Dickens' novel, Pickwick Papers. In 1965, a team led by a Doctor Gastaut(3) simultaneously recorded sleep and breathing patterns in a patient with Pickwickian Syndrome and found distinct patterns corresponding to all three types of apneas. In 1969, doctors began to treat OSA by tracheostomy. This operation involved bypassing the upper airway and mouth by cutting an opening in the trachea and inserting a breathing tube. Since then, researchers have learned a great deal more about sleep apnea, in particular how to identify the many different parts of the mouth and upper airway that may be involved in the condition. This better understanding has led to many new treatments.
The Three Types of Sleep Apnea
Central Sleep Apnea (CSA)In CSA, respiratory muscle activity simply stops for periods of time. Pure CSA is uncommon; it occurs as a result of lung problems or in people with a brain stem lesion. So-called "Cheyne-Strokes respiration" is a form of central sleep apnea found in patients with congestive heart failure, stroke, or kidney disease. The exact cause of CSA is often unknown, but recent findings suggest that enhanced sensitivity to carbon dioxide might play a pivotal role.(4)
Mixed Sleep Apnea (MSA)In MSA the breathing mechanism stops for a time. When it resumes, it is obstructed as in OSA.
Obstructive Sleep Apnea (OSA)In OSA, the lungs operate normally, but airflow is blocked because the upper airway becomes temporarily narrowed or closed. The site of obstruction may be anywhere from the nose to the glottis. Most frequently, the primary obstruction occurs in the nasopharynx, at the level of the soft palate. Unlike CSA and MSA, OSA is fairly widespread.(5) In the US, more than three million men and one and a half million women suffer from OSA, as defined by an Apnea Index of five or more, plus daytime sleepiness.
The Apnea Index equals the average number of apnea episodes per hour of sleep.
How Obstructive Sleep Apnea OccursMost people with OSA have a smaller than normal pharynx, or a pharynx that is abnormally collapsible. Normally, our pharynxes are capable of collapsing or changing shape to some degree; otherwise we would not be able to speak or swallow. When the pharynx serves as a conduit of airflow, however, it must be able to resist collapse in order to remain open. These various functions are regulated by a group of muscles that alter the shape or narrow the pharynx for swallowing or talking, but hold it open when we inhale. Even in normal people who do not suffer from OSA, sleep interferes with this regulating mechanism. It does this by(6) relaxing the upper airway muscles and dulling the reflexes that prevent the pharynx from collapsing.
Partial collapse results in snoring and, in some cases, prolonged hypoventilation, or insufficient air flow to the lungs.
Complete closure results in apnea.
The body's usual response to apnea is to wake itself enough that the muscles in the pharynx can act to clear the obstruction. These repeated or partial wakings interfere with normal sleep patterns and leave sufferers sleepy during the day.
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