Though oral breathing devices improve sleep in those with obstructive sleep apnea (OSA), new research shows the devices may not reduce risk factors associated with developing heart failure and other cardiovascular diseases.

The study was published online Jan. 27, ahead of print, in the American Journal of Respiratory and Critical Care Medicine.

In a randomized controlled trial of 150 patients with severe sleep apnea and no serious heart condition, patients were monitored while sleeping with a mandibular advancement device (MAD). Results showed though the devices improved symptoms of snoring, fatigue and sleepiness, they did not improve endothelial function or lower blood pressure.

"Endothelial dysfunction is one of the intermediate mechanisms that potentially contribute to the increased risk of cardiovascular disease in OSA," said lead study author Frédéric Gagnadoux, MD, a professor of pulmonology at the University Hospital of Angers in France, in a statement. "Whether MAD therapy improves endothelial function in OSA patients had not been evaluated before in properly controlled and adequately powered trials."

Patients in the trial, which lasted for two months, ranged in age from 18 to 70, and 86 percent were men. Gagnadoux said further studies are needed to determine if MAD therapy can improve endothelial function in sleep apnea patients.

"Our study demonstrates the effectiveness of MAD therapy in reducing sleep disordered breathing and improving related symptoms in patients with severe OSA who do not tolerate CPAP," Gagnadoux said. "Despite being affected by severe OSA, our patients' reactive hyperemia index, a validated marker of endothelial function, was within the normal range at baseline."