Dream sleep: a risk for heart patients?

To sleep: perchance to dream: ay, there's the rub/For in that sleep of death what dreams may come ....

William Shakespeare wrote of the dark side of sleep in Hamlet. Now, a team of Iowa researchers suggests that the dreaming stage of sleep poses a particular peril for people with coronary artery disease.

Humans spend about one-third of their life in sleep. Despite the popularity of sleep, scientists know very little about the physiological changes that occur during slumber. They do know that people typically pass through repeated cycles consisting of several stages of deep sleep followed by a bout of REM sleep, named for the rapid eye movements that take place at that time, when dreams occur.

In 1989, researchers at Harvard University Medical School discovered that people with arterial disease who wake up at night run the risk of ischemia, a reduction in blood flow to the heart (SN: 11/25/89, p.341). That finding fits with the observation that heart attacks often occur in the morning, just after a person wakes up. Indeed, scientists know that REM sleep occurs more frequently during the predawn hours and is associated with an activation of the sympathetic nervous system, which regulates involuntary bodily functions such as heart rate and blood pressure.

To get a detailed picture of what happens during the wee hours, Virend K. Somers and his colleagues at the University of Iowa College of Medicine in Iowa City recruited eight healthy people to spend the night in a sleep lab. The researchers hooked the recruits up to devices that recorded brain waves, heart rate, and blood pressure. By inserting electrodes into the volunteers' leg muscles, the team kept tabs on the sympathetic nervous system.

They found significantly lower heart rate, blood pressure, and sympathetic nervous system activity during nonREM sleep than during wakefulness. This is the first REM study of normal volunteers sleeping at night rather than during the day, Somers says.

The team also reports that REM sleep is associated with a surge of sympathetic nervous system activity, Indeed, these data extend the understanding of dream sleep by finding that sympathetic nervous system activity more than doubled during REM sleep. The researchers describe their findings in the Feb. 4 NEW ENGLAND JOURNAL OF MEDICINE.

"The most striking finding was the association between REM sleep and very, very high levels of sympathetic discharge," Somers says. "We think this may be a potential mechanism that explains the high incidence of heart attacks and strokes in the very early morning hours."

Of course, the Iowa group studied only healthy volunteers and thus cannot prove the link between REM sleep and heart attack risk. However, Somers and other scientists believe that the risk of heart attack starts as the sympathetic nervous system revs up -a process that makes platelets more likely to stick together and already clogged arteries more likely to spasm. During REM sleep, a blood clot may begin to form in the heart's coronary arteries. However, the heart attack doesn't occur until that clot grows large enough to shut off the heart's blood supply, perhaps several hours later, when the victim is rushing to get to work on time.

For people who think the solution to heart attack risk is to spend less time in bed, sleep researcher Richard L. Verrier of Georgetown University in Washington, D.C., warns that sleep deprivation results in a rebound effect. Sleepy people make up for lost time by going through heavy periods of REM sleep, he notes. People with artery disease may benefit from the commonsense advice to get plenty of sleep- and thus avoid heavy REM periods, he says.