Sleep apnea may predict mortality rate

Turns out, the duration of abnormal breathing events may be a better predictor of mortality risk in both women and men.

Obstructive sleep apnea (OSA) is the temporary cessation of breathing during sleep.

According to new research published in the American Journal of Respiratory and Critical Care Medicine, participants who had short apneas and hypopneas (stopped breaths and shallow breaths, respectively) were at greater risk of dying over a decade of follow up.

"This result seems counter-intuitive because you might expect longer periods of not breathing to be more severe," said study's lead author, Dr. Matthew P. Butler. "On the other hand, shorter periods of disturbed breathing indicate a low arousal threshold, which would associate with sleep fragmentation, elevated sympathetic tone and greater risk for hypertension."

Previous studies have shown that the apnea-hypopnea index (AHI), the most widely used measure of sleep apnea severity, is linked to mortality and heart disease. However, according to the recent research, AHI remains a coarse measure of sleep apnea severity and is not a good risk predictor for women.

The duration of these events, the authors wrote, is easily determined from the same polysomnography studies that patients now undergo to measure AHI.

They analysed the records of 5,712 adults (average age 63) who participated. This community-based study enrolled an approximately equal number of men and women and followed them for up to 11 years.

The study found that participants with the shortest duration of breathing events were 31 per cent more likely to die and this association was strongest in participants with moderate sleep apnea as measured by AHI. In this group, participants with the shortest duration of breathing events had a 59 percent increased risk of dying.

The findings indicated that there may be several mechanisms by which sleep apnea leads to increased mortality and a need to measure several features associated with apnea occurrence. In particular, apneas of different types and event durations may result in adverse health outcomes.

According to the researchers, these findings suggest a phenotype of OSA that may be genetically encoded. They add that other studies have shown that the duration of breathing events is highly heritable and that shorter abnormal breathing events are more common in women.