"For decades, we have blamed sleep apnea solely on a narrowed airway caused by enlarged tonsils, a small jaw or excess fat in the throat," said Dr. Ronald Harper, principal investigator and professor of neurobiology at the David Geffen School of Medicine at UCLA. "Our findings show, however, that sleep apnea patients also suffer disordered wiring in brain regions that control muscles of the airway. These glitches may lead to the syndrome, which is exacerbated by a small airway."
Harper's team used magnetic resonance imaging (MRI) to compare brain structures of 21 men who had been diagnosed with sleep apnea to 21 men who did not suffer from the disorder. Then they weighed their findings against a template derived from 152 normal MRI scans obtained from the Montreal Neurological Institute.
Both sets of men were matched for age and weight. The researchers also considered the effects of disease severity, tobacco use, hypertension, cardiovascular health and whether the men were left- or right-handed in their comparison.
The MRIs revealed dramatic gray matter loss in the brains of the men with sleep apnea. Curiously, the tissue loss occurred primarily in regions of the brain that control speech production, movement and emotion. The amount of brain damage directly correlated to the severity of the patient's disorder. The healthy men's brains ranged from 2 percent to 18 percent larger in these areas than the men with sleep apnea.
"We propose that early damage to the brain's speech center triggers problems in the muscles that control the airway," said Dr. Paul Macey, first author and assistant researcher of neurobiology at the David Geffen School of Medicine at UCLA. "This, in turn, eventually leads to sleep apnea."
"Our findings suggest this sleep apnea is a pre-existing condition -- that abnormal brain wiring from childhood contributes to the onset of the disorder in adulthood," Harper said. "The evidence in the brain is very specific."
Harper noted that obstructive sleep apnea patients often display other traits that suggest subtle brain damage, including problems with memory, thought and motor skills. "The repeated oxygen loss from sleep apnea may damage other brain structures that regulate memory and thinking," he said.
The UCLA researchers uncovered another intriguing finding. In an online supplement to their article, Harper and Macey wrote that 38 percent of the sleep apnea patients reported a history of stuttering or speech impairment. Most of the men had struggled with word-formation problems since childhood, and some still had language difficulties as adults.
The incidence of stuttering in the general population is 7 percent.
"Because the sleep apnea patients possessed speech impairments from childhood and their brain's speech center revealed significant gray matter loss, this brain damage likely originated early in life," Macey said.
The next step will be to examine the brain structures of children afflicted with obstructive sleep apnea, who may not have battled the disease long enough to develop the brain damage found in adults.
"Speech impediments may prove an important diagnostic clue for assessing and treating sleep apnea," Macey said. "In the future, doctors may monitor certain brain structures and examine children for speech or movement problems that may predict a higher sleep apnea risk."
Nearly 4 percent of the U.S. population suffers from obstructive sleep apnea, which causes explosively loud snoring at night and extreme sleepiness during the day. People who suffer from the disorder constantly struggle to breathe during sleep, because their throat and mouth relax to such a degree that their airway collapses. They wake up to begin breathing, then repeat the cycle throughout the night, seriously disrupting their sleep.
The loss of oxygen and the constant struggle to breathe increase sleep apnea patients' risk of high blood pressure, stroke and other heart-related ailments. The disorder is most common in men, the elderly, the obese and children with large tonsils -- but not all people with these characteristics develop the disease.
The National Heart, Lung and Blood Institute supported the UCLA study. Harper and Macey's co-authors included Luke Henderson, Katherine Macey, Jeffry Alger, Robert Frysinger, Mary Woo, Rebecca Harper and Frisca Yan-Go.
Journal
American Journal of Respiratory and Critical Care Medicine