The connection between sleep apnea and heart disease is evolving very rapidly. People with cardiovascular problems such as high blood pressure, heart failure, and stroke have a high prevalence of sleep apnea. Whether sleep apnea actually causes heart disease is still unclear, but we do know that if you have sleep apnea today, the chance that you will develop hypertension in the future increases significantly.

One of the problems in defining the relationship between sleep apnea and heart disease is that people with sleep apnea often have other co-existing diseases as well.

If you treat people with high blood pressure and sleep apnea, or heart failure and sleep apnea, the measures of blood pressure or heart failure are significantly improved. There is good evidence to think there is a cause-and-effect relationship between hypertension and sleep apnea.

Why does your blood pressure go up when your sleep is disrupted by sleep apnea?Your blood pressure will go up because when you're not breathing, the oxygen level in your body falls and excites receptors that alert the brain. In response, the brain sends signals through the nervous system and essentially tells the blood vessels to "tighten up" in order to increase the flow of oxygen to the heart and the brain, because they have priority.

The problem is that things that go on at night tend to carry over in the daytime, even when the sleep apnea patient is awake. The low oxygen levels at night seem to trigger multiple mechanisms that persist during the daytime, even when the patient is breathing normally.

How can CPAP (continuous positive airway pressure) reduce the cardiovascular consequences of sleep apnea?The available evidence tells us that when you treat people with sleep apnea using CPAP, their blood pressure is not only lower at night—it's also lower during the day. That's a very good thing. Moreover, people with atrial fibrillation [a common type of irregular heart beat] with sleep apnea that is appropriately treated have only a 40% chance of coming back for further treatment of their atrial fibrillation. If their sleep apnea is untreated, the chance of a recurrence of atrial fibrillation goes up to 80%. The message to heart patients with sleep apnea is: With treatment of your sleep apnea, your chances of improvement are considerably better.

Dr. Somers is Professor of Internal Medicine in the Division of Cardiovascular Diseases at the Mayo Clinic in Rochester, MN.

This article originally appeared in the Summer 2004 issue of sleepmatters and is reprinted by the National Sleep Foundation for educational use by its readers.