President Joe Biden in recent weeks has started using a continuous positive airway pressure, or CPAP, machine at night to help with sleep apnea, the White House said Wednesday. The revelation comes after indents from the mask were visible on the president’s face as he departed the White House.

The president has disclosed since 2008 a history with sleep apnea, a potentially serious but common condition in which breathing can stop and start in the night. Biden used the machine Tuesday night, White House officials said. The imprint lines on his face were apparent when he left Wednesday morning for a speech in Chicago.

A CPAP machine is a motorized device that pumps air through a mask to open a sleeper’s airway. About 5 million Americans have tried them.