A medical condition in which the patient stops breathing while asleep due to problems with signals in the brain that control breathing. It can be detected by a medical procedure known as a polysomnogram.
Central Sleep Apnea is actually somewhat rare, especially compared to its far more common sibling, Obstructive Sleep Apnea (OSA), which is suspected to affect up to 10% of the population in some form or another.
With Obstructive Sleep Apnea, the tongue, uvula, pharynx, or some other soft tissue settles over the patient's windpipe while s/he is asleep, blocking off the air and making it difficult for the patient to breathe. This problem, while widespread and highly annoying, is imminently treatable through the use of surgery (see the uvulopalatopharyngoplasty writeup under Obstructive Sleep Apnea) or via pressure mask systems like CPAPs and BiPAPs.
Central sleep apnea, however, is far more dangerous and far more difficult to treat. It can be caused by brain stem lesions, encephalitis affecting the brain stem, various neurodegenerative illnesses, strokes, and complications of surgery of the cervical spine. There are also anecdotal accounts of victims of direct lightning strikes becoming victims of this disorder, as if the immense shock of electricity "shorted out" their body's own ability to regulate their sleep/wake cycle.
Because central sleep apnea (as opposed to OSA) is not caused by a physical blockage, positive air pressure machines like CPAP and BiPAPs are ineffective and surgery is fairly useless as a treatment. Patients with mild central sleep apnea sometimes respond to low doses of the tricyclic antidepressant Protriptyline (Triptil, Vivactil), which seems to stimulate breathing with some patients. Other patients, paradoxically enough, find some relief in taking small doses (0.5 - 1mg) of Clonazepam (Klonopin), a depressant medication.
While low doses of oxygen have been shown to limit the number of apneaic events in some patients, victims of severe Central Sleep Apnea often have to be placed on ventilators to ensure they continue to breathe while asleep. It is truly a life-threatening condition and, unfortunately--especially in the severe cases--there is often little that can be done in the way of treatment for the disorder at this time.