Sleep Apnea and Heart Disease

Washington, DC - March 28, 2001

One underlying cause of heart disease, high blood pressure, or other heart problems may be sleep apnea. Dr. Virend Somers spoke to the issue of sleep apnea and heart disease at the Science of Mind-Body Interactions conference held at the National Institutes of Health. He suggested that "Physicians should look for sleep disorders in patients with congestive heart failure or hypertension, especially if they are not responding to standard therapy".

In his talk to conference delegates, Dr. Somers, professor of hypertension and cardiology at the Mayo Clinic in Rochester, Minnesota, pointed out that there is a strong association between obstructive sleep apnea (OSA) and hypertension, heart failure, stroke and ischemic heart disease. Research has shown that OSA patients with normal blood pressure run a risk of developing high blood pressure within four years. Hypertension is a major risk factor in the development of heart disease and stroke.

Somers and his colleagues have done research on OSA patients who had no other illnesses, to rule out any confounding factors. They found that apnea patients have higher levels of sympathetic nervous system (SNS) activity during both wake and sleep than a matched set of control patients without OSA. Involuntary functions such as heart rate and blood vessel constriction are controlled by the sympathetic nervous system. In persons without apnea, there is usually a decrease in SNS activity and blood pressure falls when sleeping.

However, during apnea events, the higher level of SNS activity constricts the blood vessels, while the heart rate also jumps, slamming blood into tight vessels. Blood pressure spikes of up to 250/150 have been seen during apneas.

Sleep apnea patients also have faster heart rates than non-apnea patients, even when awake, but have less variability in their heart rates. This combination of a less variable heart rate and greater variability in blood pressure is an indicator of potential cardiovascular problems.

Apnea patients also produce higher levels of endothelin and lower levels of nitric oxide. This results in more constriction and less relaxation of blood vessels. Dr. Somers said that after only four hours of sleep, an untreated apnea patient's levels of endothelin can rise up to 50%. When treated, usually with CPAP (continuous positive airway pressure), endothelin levels return to normal. This elevated endothelin is believed to impair blood pressure regulation as well.

Summary

As sleep apnea patients stop breathing, their oxygen levels decrease and their carbon dioxide levels correspondingly increase, which activates the sympathetic nervous system. When the apnea patients breathe in, their cardiac output increases and their blood pressure spikes. This disrupts the normal nighttime regulation of blood pressure and the sympathetic nervous system. These factors seem to be implicated in the increased incidence of cardiovascular problems in sleep apnea patients.

For a similar report from Dr. Somers, see Sleep Apnea Impairs Blood Pressure Regulation