Obstructive sleep apnea (OSA) is associated with increased sympathetic nerve activity (SNA) and blood pressure (BP) even when awake. This study compared 10 patients with OSA to 10 age- and sex-matched control subjects and 5 obese subjects without OSA. Patients with OSA had significantly higher SNA and BP levels when awake compared to controls. During sleep, SNA and BP increased further, especially during stage II and rapid eye movement (REM) sleep. These increases were most pronounced during apneic events, with peak SNA reaching 299% of wakefulness levels during stage II sleep and 246% during REM sleep. Continuous positive airway pressure (CPAP) treatment reduced SNA and BP during sleep, suggesting that OSA contributes to these sympathetic and cardiovascular responses. The study found that OSA patients had higher sympathetic activity and BP levels during sleep compared to normal sleep, even though they already had high levels of sympathetic activity when awake. Apneic episodes caused progressive increases in sympathetic activity, which were most marked at the end of the apnea. With the resumption of breathing, sympathetic activity abruptly ceased, and BP increased. This pattern was not observed in normal sleep, where BP and SNA typically decrease during non-REM sleep. CPAP treatment reduced sympathetic activity and BP during sleep, indicating that it helps to alleviate the sympathetic and cardiovascular responses associated with OSA. The study suggests that OSA, rather than obesity alone, is responsible for the increased sympathetic activity and BP during sleep. The mechanisms underlying these responses involve chemoreflexes, baroreflexes, and the pulmonary afferents, which are activated during apneic episodes. These reflexes contribute to the oscillations in BP and SNA observed during OSA. The findings highlight the importance of treating OSA to prevent the long-term cardiovascular complications associated with chronic sympathetic activation. CPAP therapy is effective in reducing sympathetic activity and BP during sleep, thereby improving cardiovascular outcomes in OSA patients.Obstructive sleep apnea (OSA) is associated with increased sympathetic nerve activity (SNA) and blood pressure (BP) even when awake. This study compared 10 patients with OSA to 10 age- and sex-matched control subjects and 5 obese subjects without OSA. Patients with OSA had significantly higher SNA and BP levels when awake compared to controls. During sleep, SNA and BP increased further, especially during stage II and rapid eye movement (REM) sleep. These increases were most pronounced during apneic events, with peak SNA reaching 299% of wakefulness levels during stage II sleep and 246% during REM sleep. Continuous positive airway pressure (CPAP) treatment reduced SNA and BP during sleep, suggesting that OSA contributes to these sympathetic and cardiovascular responses. The study found that OSA patients had higher sympathetic activity and BP levels during sleep compared to normal sleep, even though they already had high levels of sympathetic activity when awake. Apneic episodes caused progressive increases in sympathetic activity, which were most marked at the end of the apnea. With the resumption of breathing, sympathetic activity abruptly ceased, and BP increased. This pattern was not observed in normal sleep, where BP and SNA typically decrease during non-REM sleep. CPAP treatment reduced sympathetic activity and BP during sleep, indicating that it helps to alleviate the sympathetic and cardiovascular responses associated with OSA. The study suggests that OSA, rather than obesity alone, is responsible for the increased sympathetic activity and BP during sleep. The mechanisms underlying these responses involve chemoreflexes, baroreflexes, and the pulmonary afferents, which are activated during apneic episodes. These reflexes contribute to the oscillations in BP and SNA observed during OSA. The findings highlight the importance of treating OSA to prevent the long-term cardiovascular complications associated with chronic sympathetic activation. CPAP therapy is effective in reducing sympathetic activity and BP during sleep, thereby improving cardiovascular outcomes in OSA patients.