BETHESDA, MD—If you’ve got a heart disease patient who doesn’t seem to get better no matter what you do, consider the possibility that he or she is suffering from sleep apnea, said Virend Somers, MD, at a conference on mind-body medicine held at the National Institutes of Health.
“Doctors who are trying to understand and treat disease are focused mainly on wakefulness. What happens during sleep is instrumental in treating disease, especially cardiovascular disease,” Dr. Somers said. “Physicians should look for sleep disorders in patients with congestive heart failure or hypertension, especially if they are not responding to standard therapy.”
In studies of patients with sleep apnea and no other illnesses, Dr. Somers and colleagues found that the apneic patients had higher sympathetic nervous system activity during both sleep and waking periods, compared to a group of control patients who were matched for age, gender, and body mass index. Those with apnea were more likely to develop hypertension within four years, said Dr. Somers, who is professor of hypertension and cardiology at the Mayo Clinic in Rochester, Minn.
“When [healthy] patients are in non-rapid-eye-movement (non-REM) sleep, their sympathetic nervous activity decreases and their blood pressure falls,” he explained. “But with apnea, patients stop breathing, their oxygen levels go down and their carbon dioxide levels go up, resulting in activation of the sympathetic nervous system.”
When they become hypoxic, their peripheral chemoreceptors are activated. Increased carbon dioxide activates the central chemoreceptors, “so you have a synergistic sympathetic activation, explained Dr. Somers. “There’s reason to suppose that when you have sleep apnea and you’re not breathing, your sympathetic activity’s going to get even higher.
[Then] when apneic subjects do breathe in, “their cardiac output increases and their blood pressure skyrockets, disrupting the normal regulation of the sympathetic activity and blood pressure that we would expect through the night.” Dr. Somers and his colleagues have found that apnea patients who do not have hypertension had an average intra-arterial blood pressure of 130/60 mmHg during the day. But during an apneic episode, it went up as high as 250/140 mmHg. “This is an extraordinarily high level of stress inflicted on the blood vessels repetitively during the night.”
Apnea patients also have less variation in heart rate along with their greater variability in blood pressure, Dr. Somers said. “Both of these things are bad and can predict cardiovascular disease down the road.” These patients also have higher levels of endothelin, “the most potent vasoconstrictor that the body produces.”
Even in the absence of overt cardiovascular disease, people with obstructive sleep apnea show impairment in resistance-vessel endothelium-dependent vasodilation. Dr. Somers and his colleagues compared forearm blood flow responses to infusions of acetylcholine in otherwise healthy apneic patients versus obese but otherwise healthy controls. The patients with apnea had significantly blunted vasodilatory responses to the acetylcholine (Kato M, et al. Circulation 2000;102(21): 2607–10).
Many of the sleep apnea patients’ problems can be helped with the use of a continuous positive airway pressure (CPAP) device, which is the standard treatment for sleep apnea. Over time, it appears that CPAP can reduce sympathetic nerve traffic. But this takes at least 6 months of therapy (Narkiewicz K, et al. Circulation 1999; 100(23):2332–5).
Still unsure which patients to screen for sleep apnea? Individuals with this condition are often obese and may also exhibit hypertension and daytime somnolence, as well as a narrow esophageal airway, Dr. Somers noted.
