Dr. Belen Esparis, medical director of the Mount Sinai Medical Center Sleep Disorders Center, has seen patients who have been in car accidents after falling asleep at the wheel and others who have developed abnormal heart rhythms.
The common denominator? They all suffer from obstructive sleep apnea, a common sleep disorder characterized by interruptions in breathing during sleep, which can occur as many as 100 times per hour.
The sleeping disorder mostly affects people 40 and older, often who are overweight. More men than women suffer from the sleeping disorder, but it becomes more common among both sexes as they age.
Sleep apnea is known to cause a range of cardiovascular, neurological and behavioral problems, including high blood pressure, heart attacks, poor memory, lack of concentration and depression.
It is also known to be a risk factor for strokes.
“More than just correlating them, we really want to understand why one leads to the other,” said Dr. Alberto Ramos, co-director of the UHealth Sleep Disorders Program at the University of Miami, who is conducting research on what makes sleep apnea a risk factor for strokes.
A stroke occurs when the blood supply to part of the brain is interrupted, depriving the brain of oxygen. A stroke may be caused by a narrowed or blocked artery supplying blood to the brain or by a burst blood vessel in the brain.
The interruptions in breathing that characterize sleep apnea lead to low oxygen levels in the blood and brain.
“Sleep apnea triggers a series of responses in the body as a result of low oxygen levels,” Ramos said. “One of them is hypertension — an increase in blood pressure.”
Hypertension associated with sleep apnea occurs because of the strain that low oxygen levels in the blood and brain place on the cardiovascular system. As high blood pressure is an independent risk for stroke, sleep apnea becomes an indirect cause of stroke.
Sleep apnea is most likely to lead to ischemic strokes, the ones caused by an interruption of blood supply to the brain.
High blood pressure can cause hardening or narrowing of the arteries, according to Ramos, which sometimes restricts blood flow to organs and tissues. Narrowed arteries are more prone to plaque buildup, which can further restrict blood flow.
“This process may progressively clog arteries over time. When you don’t have blood flow to the arteries, that can manifest as a stroke,” Ramos said.
Although sleep apnea causes low oxygen levels in the body and leads to a host of other complications, the sleep disorder itself is not fatal and does not directly cause stroke.
“Sleep apnea is one step removed from the heart attack or stroke — it’s what the sleep apnea does to the circulatory system and heart that causes the stroke,” said Dr. Sachin Rastogi, a radiologist in the Division of Interventional Neuroradiology at Mount Sinai Medical Center in Miami Beach.
According to Rastogi, when the body is deprived of oxygen, as is the case with obstructive sleep apnea, the body releases catecholamines — a type of adrenaline — to get the airway open. Catecholamines constrict blood vessels, and constricted blood vessels can lead to hypertension.
It is important to note that the effect of sleep apnea on the circulatory system and all the bodily processes associated with low oxygen levels and hypertension will not put people at risk for stroke from one day to the next.
“It takes several years or decades of all these things running in the background to make a stroke happen,” Rastogi said. He mostly sees patients between the ages of 50 and 90 who have already suffered a stroke.
Obesity and age are two of the risk factors associated with obstructive sleep apnea, but those who are thin and young are also at risk.
In the case of people who are not overweight, sleep apnea can be caused by having a long tongue, a narrow jaw, or a long uvula, which is the punching-bag looking tissue that hangs from the back of the throat.
Sleep apnea in children is related to them having large tonsils, the tissues seen on either side of the throat at the back of the mouth, and large adenoids, small tissues located behind the nasal cavity. In kids, sleep apnea is usually easily treated by surgically removing the tonsils and adenoids.
However, with the recent childhood obesity epidemic, pediatric sleep disorders are not solely caused by large tonsils.
“Health issues that once belonged only to adults are now being seen in children,” said Dr. Sayed Naqvi, a neurologist and stroke medical director at Miami Children’s Hospital. “Bad habits — eating poorly, smoking and abusing alcohol— developed illnesses in adults slowly. Now young people are carrying adult bad habits and developing adult illnesses.”
Poor eating habits among families contribute to child obesity, and some of Naqvi’s adolescent and teenage patients suffer from sleep apnea for the reasons a middle-aged person would.
To eliminate the potential for strokes and other risks associated with low oxygen levels in the body, sleep apnea must be treated. Continuous positive airway pressure machines, known as CPAP, use nose masks and a hose connected to the machine to deliver pressurized air to the lungs.
For overweight patients, the solution to sleep apnea and all the associated risks is losing weight.
“I don’t consider losing weight an alternative treatment,” Esparis said. “It’s a standard of care.”
Ramos tells his patients to take care of their sleep and to adopt good sleep habits — no caffeine close to bedtime, no watching television in bed, darken the room and set the thermostat at a comfortable temperature to keep from tossing and turning.
“We think of sleep as the third leg of this tripod of health — for a healthy lifestyle you need to sleep well, do exercise and eat well,” Ramos said. “We try to push those three things for our stroke patients and all our patients.”