People with obstructive sleep apnea (OSA) may be able to increase the volume of gray matter in their brains by undergoing continuous positive airway pressure therapy, also known as CPAP, new research indicates.

Researchers in Italy, in a study involving 17 patients with obstructive sleep apnea and 15 healthy people, found that patients with OSA had reductions of gray matter volume and an associated decrease in neuropsychologic performance. But after three months of CPAP therapy, the OSA patients showed a significant increase in gray matter volume and in neuropsychologic testing. No further improvement in gray matter volume was noted when patients were re-evaluated after one year of CPAP therapy.

Obstructive sleep apnea is a sleep-related breathing disorder that involves a decrease or temporary halt in airflow, despite an ongoing effort to breathe. It occurs when the muscles relax during sleep, causing soft tissue in the back of the throat to collapse and block the upper airway.

This leads to partial reductions and complete pauses in breathing that can produce abrupt reductions in blood oxygen levels and reduce blood flow to the brain. CPAP therapy corrects low levels of oxygen in the blood and reduces pauses in breathing. CPAP provides a steady flow of air through a facemask that is worn while sleeping.

According to the National Institute of Neurological Disorders and Stroke, gray matter refers to the cerebral cortex, where the brain does most of its processing of information. It has a gray-colored appearance because it lacks the myelin insulation that makes most other parts of the brain look white.

Sleep Apnea and Gray Matter
In the study, magnetic resonance imaging and a technique called voxel-based morphometry were used to scan brains and describe differences in gray matter. At the beginning of the study, patients with OSA had reductions in gray matter volume in several regions of the brain. Significant increases in gray matter volume were noted after three months of CPAP therapy in specific regions of the brain -- the hippocampus and frontal areas.

The increase of gray matter volume in these regions is specifically correlated with the improvement at neuropsychological tests of executive functioning and short-term memory," says principle investigator Vincenza Castronovo, PhD, sleep laboratory coordinator at the University Vita-Salute San Raffaele and San Raffaele Scientific Institute in Milan, Italy.

Castronovo says that measuring neuropsychological performance may help doctors assess patients with obstructive sleep apnea to determine the effectiveness of treatment.

"Our results also suggest that specific neuropsychological measures are valuable tools for the assessment of therapy success and can offer to patients and physicians the evidence that adherence to treatment can lead not only to clinical but also to brain-structural recovery" of people with obstructive sleep apnea, Castronovo says.

Gray matter deficits in people with obstructive sleep apnea also were reported in the February 2010 issue of the journal Sleep. A French study published in the March 2009 issue of the Journal of Sleep Research reported gray matter loss in multiple brain regions in patients with obstructive sleep apnea.

Castronovo and colleagues say their study provides evidence that CPAP therapy works and offers hope to obstructive sleep apnea patients.