Recordings of sympathetic nerve activity (SNA), respiration (RESP) and intra-arterial blood pressure (BP) in the same subject when awake (top left), with obstructive sleep apnea (OSA) during rapid eye movement (REM) sleep (bottom), and with elimination of obstructive apnea by continuous positive airways pressure (CPAP) therapy during REM sleep (top right). SNA is very high during wakefulness, but increases even further secondary to OSA during REM. BP increases from 130/65 mmHg when awake to 256/110 mmHg at the end of apnea. Overall, nocturnal blood pressure is increased. Elimination of apnea by CPAP therapy (top right) results in decreased sympathetic traffic and prevents BP surges during REM sleep. Reproduced with permission from .