Sleep apnea may boost blood carbon dioxide levels

By David Douglas

NEW YORK (Reuters Health) - People who suffer from the nighttime breathing disorder known as sleep apnea may develop high levels of carbon dioxide in the blood during the daytime -- a condition known as hypercapnia, Japanese researchers have found.

Dr. Koichiro Tatsumi from Chiba University and colleagues studied 1,227 patients with obstructive sleep apnea -- a common problem in which people stop breathing for short periods during sleep. It occurs when soft tissues in the back of the throat collapses, temporarily block the airway.

Tests showed that 168 of the patients, or 14 percent, suffered from daytime hypercapnia. These patients weighed significantly more and had worse sleep apnea than patients with normal blood levels of carbon dioxide.

Tatsumi's team went on to study the effect of a standard treatment for sleep apnea called continuous positive airway pressure (CPAP) therapy in 37 "hypercapnic" patients who had severe sleep apnea. With CPAP, a special face mask is worn that continuously blows air into the throat, preventing the tissues from collapsing.

At 3 months, CPAP had corrected daytime hypercapnia in 19 (51 percent) of these patients, the researchers report.

The finding that about half of patients sleep apnea and high blood carbon dioxide levels respond to CPAP therapy suggests that the two conditions are related; "daytime hypercapnia in sleep apnea syndrome may be an end-product of a complex conglomerate," Tatsumi told Reuters Health.

The study findings are published this month in the medical journal Chest.

In a commentary on the study, Drs. Clifford Zwillich and Carolyn H. Welsh of Denver Veterans Affairs Medical Center, Colorado, note that although this study was conducted in a Japanese population, it may suggest that "hundreds of thousands of increasingly obese Americans are at risk for severe disease, associated hospitalizations, and possibly premature death."

SOURCE: Chest, December 2007.