By Anthony J. Brown, MD

NEW YORK (Reuters Health) - A treatment called CPAP can virtually eliminate a particular type of nighttime breathing disorder called central sleep apnea. However, it does not seem to reduce sleep awakenings or improve sleep quality, a study indicates.

People with sleep apnea involuntarily stop breathing dozens of times each night, causing them to gasp for breath. Obstructive sleep apnea occurs when the airway becomes blocked by tissue such as the tonsils or base of the tongue, whereas central sleep apnea occurs when the respiratory system stops working in the absence of a blockage.

CPAP, which stands for continuous positive airway pressure, is a method of respiratory ventilation in which a gentle continuous stream of air is delivered through a pliable mask worn over the nose during sleep.

The finding that CPAP does not curb sleep awakenings or improve sleep quality in central sleep apnea patients was surprising and runs counter to what is seen with obstructive sleep apnea, senior researcher Dr. T. Douglas Bradley, from Toronto General Hospital, told Reuters Health. With obstructive disease, CPAP "causes a marked reduction in sleep disruption and improvement in sleep quality."

"Prior to this study, it had always been thought brief awakenings from sleep (arousals) were an important defense mechanism that terminated apneas during sleep, thus preventing asphyxia," he noted. "However, studies examining this issue were largely focused on obstructive sleep apnea."

The current results, reported in the journal Sleep, suggest that sleep arousals are not, in fact, a defensive mechanism with central sleep apnea. Instead, these arousals may be a cause of central sleep apnea, Bradley said.

The study involved 205 heart failure patients with central sleep apnea who were randomized to receive optimal medical therapy with or without CPAP. Tests were performed at the start of the study and at 3 months.

No change in apnea episodes or in sleep arousals was seen in the control group. In the CPAP group, apnea episodes decreased significantly, but, as noted, no change in sleep awakenings or sleep quality occurred.

"Sleep disruption by frequent awakenings may have previously unrecognized harmful effects in patients with heart failure," Bradley said. Because central sleep apnea has been linked to an increased risk of death in heart failure patients, he added, it will be important in future studies to determine if preventing sleep arousals in these patients might alleviate central sleep apnea and also reduce mortality.

SOURCE: Sleep, January 2009.

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