September 1, 2006 — Mayo Clinic researchers have discovered a new type of sleep apnea dubbed complex sleep apnea. The findings will be published in the September issue of the journal Sleep.
The two previously known types of sleep apnea include obstructive sleep apnea and central sleep apnea. In obstructive sleep apnea, the more common form, the throat muscles relax and the airway is narrowed, momentarily cutting off breathing and resulting in noisy snoring. With central sleep apnea, the brain does not send proper signals to the muscles that control breathing. The newly discovered type, complex sleep apnea, is a combination of both obstructive and central sleep apneas.
Patients with complex sleep apnea at first appear to have obstructive sleep apnea and stop breathing 20 to 30 times per hour each night. But unlike typical obstructive sleep apnea patients, their breathing problem is not completely alleviated by CPAP (continuous positive air pressure), which functions like a pneumatic splint to open a patient’s airway. Instead, once the CPAP is applied to complex sleep apnea patients, the obstruction seems to dissipate, but still the patients do not breathe properly. Symptoms of central sleep apnea then appear and fragmented sleep results, due to frequent pauses in breathing.
“All of us in our sleep lab have observed for years that there are patients who appear to have obstructive sleep apnea, but the CPAP doesn’t make them all that much better—they still have moderate to severe sleep apnea even with our best treatment and subjectively don’t feel they’re doing very well,” says Timothy Morgenthaler, MD, Mayo Clinic sleep medicine specialist, pulmonologist, and lead study investigator. “When they put on a CPAP machine, they start to look like central-sleep apnea syndrome patients. This phenomenon has been observed for years, but this study is the first attempt to categorize these people.”
The study involved a retrospective review of 223 patients consecutively referred to the Mayo Clinic Sleep Disorders Center over one month, plus 20 consecutive patients diagnosed with central sleep apnea. The investigators found that complex sleep apnea comprised 15% of all sleep apnea patients, while 84% had obstructive sleep apnea and 0.4% had central sleep apnea. They also discovered that males have a higher tendency to have complex sleep apnea. Morgenthaler says this may be due to less stable respiratory control in males than females. The complex sleep apnea patients had sleep and cardiovascular histories similar to the obstructive sleep apnea patients. The complex sleep apnea patients also had fewer complaints about waking up after initially falling asleep than those with central sleep apnea (32% vs. 79%). The investigators found that complex sleep apnea could be diagnosed based on patients’ sleep patterns defined at their initial diagnostic exams plus lack of response to CPAP.
According to Morgenthaler, no known factors influence risk for complex sleep apnea. An effective treatment has not been identified, but research continues to test breathing assistance machines to alleviate this condition’s symptoms.