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School of Medicine
- Study is the first to quantify death rates for sleep apnea, especially in people who snore
Nightly bouts of interrupted, oxygen-deprived sleep from a collapsed airway in the upper neck raises the chances of dying in middle-aged to elderly people by as much as 46 percent in the most severe cases, according to a landmark study on sleep apnea by lung experts at Johns Hopkins and six other U.S. medical centers.
Even in people with moderate forms of the sleeping disorder, with anywhere from 15 to 30 episodes of interrupted breathing during each hour of supposed rest, risk of death jumps 17 percent.
The ongoing study is believed to be the largest ever conducted into sleep and related illnesses, with the latest report taking more than a decade to complete. The study involves some 6,441 men and women between ages 40 and 70, with mild to severe forms of sleep apnea or none at all. Many are self-described snorers; snoring is a key symptom of sleep apnea.
Though anecdotal reports and medical record searches have long hinted at the connection between sleep problems and death, especially from heart disease, the latest study is the first to define death from sleep apnea by monitoring a large number of people with or without the sleeping condition, including a high proportion of snorers, to see who dies and who does not. Some 1,047 deaths occurred among study participants since the clinical investigation began. It is estimated that 24 percent of American men and 9 percent of women have irregular breathing patterns during sleep, with four in five unaware that they have a problem.
As part of the so-called Sleep Heart Health Study, researchers at Johns Hopkins Bayview Medical Center monitored study participants' sleep patterns at home for at least one full night's sleep, which averaged about seven hours. More than 50 study technicians were needed to handle the nearly 10,000 detailed recordings of participants' breathing patterns, heart rhythms and brain activity made to date. About half of all participants had moderate to severe sleep apnea. They were then tracked through annual clinic visits to gauge any sickness or death from high blood pressure, heart disease or stroke.
Reporting it the Public Library of Science, Medicine online Aug. 18, researchers found that as little as 11 minutes a night - just 2 percent of an average night's sleep of seven hours - spent in severe sleep apnea and subsequent oxygen deprivation, in which blood oxygen levels drop below 90 percent, doubled the death rate in men.
Women in the study who died and had severe sleep apnea were too few for researchers to draw a similar conclusion at this stage in the study, but researchers suspect that further research will bear the same results.
"Our study results really raise concern about the potentially harmful effects of sleep apnea," says pulmonologist and study site principal investigator Naresh Punjabi, M.D., Ph.D., an associate professor at the Johns Hopkins University School of Medicine. He adds that low blood oxygen levels during sleep are "a particularly worrisome sign," citing the factor as the single biggest predictor of death in people with sleeping disorders.
"Such an increased risk of death warrants screening for sleep apnea as part of routine health care, in which all physicians should inquire about patients' sleeping habits, including symptoms of feeling tired or drowsy during the daytime, poor nighttime sleep quality, recurrent awakenings from sleep, and reports from your bed partner that you snore loudly or intermittently stop breathing during the night," says Punjabi.
He says that given how widespread sleep apnea is, acquiring this information is relatively easy and essential for medical scientists to identify which, if any, particular treatments work at curing the illness by ultimately lowering the number of chronic medical conditions and premature deaths caused by it.
Key among such treatments is use of overnight sleeping aids, such as the CPAP (continuous positive airway pressure) device. The device, which resembles a typical oxygen mask, is worn over the nose and connected by a thin tube to a machine that forces air into the nasal passages, preventing the airways from collapsing.
"Our goal is to achieve normal breathing patterns during sleep and maintain blood oxygen levels as close to normal as possible," says Punjabi, who points out that the medical standard is to always maintain blood oxygen levels in the range of 95 percent or above.
Punjabi says the study team's next steps are to separate causes of death due to sleep apnea, in particular, defining the added risk from heart disease or stroke.
Funding support for the study was provided by the National Heart, Lung and Blood Institute, a member of the National Institutes of Health.
Besides Punjabi, other Johns Hopkins researchers involved in the study were Brian Caffo, Ph.D.; Philip Smith, M.D.; Moyses Szkio, M.D., Ph.D.; and Melissa Minotti. Johns Hopkins was also the data coordinating center for the Sleep Heart Health Study, with additional research assistance provided by Marie Diener-West, Ph.D.; John Dodge; Michele Donithan, M.H.S.; Charlene Levine, B.S.; Curtis Meinhart, Ph.D.; Nancy Min, M.H.S., M.P.H., Ph.D.; Michael Smith, B.S.; Andrea Tibbs, B.S.; James Tonascia, Ph.D.; Linda Roberts, M.H.S.; and Jill Meinert.
Other study co-investigators involved in writing the report were James Goodwin and Eyal Shahar at the University of Arizona, Daniel Gottlieb and George O'Connor at Boston University, Anne Newman and David Unruh at the University of Pittsburgh, David Rapaport at New York University, Susan Redline at Case Western Reserve University, Helaine Resnick at the American Association of Homes and Services for the Aging, and David Samet at the University of Southern California.
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